diff --git a/build.rs b/build.rs
index 3176abd157..dff3527127 100644
--- a/build.rs
+++ b/build.rs
@@ -205,6 +205,7 @@ fn ignore(testsuite: &str, testname: &str, strategy: &str) -> bool {
 
             // Still working on implementing these. See #929.
             ("reference_types", "table_copy_on_imported_tables") => return false,
+            ("reference_types", "externref_id_function") => return false,
             ("reference_types", _) => return true,
 
             _ => {}
diff --git a/crates/c-api/macros/src/lib.rs b/crates/c-api/macros/src/lib.rs
index 304b95c4e9..1ca2655660 100644
--- a/crates/c-api/macros/src/lib.rs
+++ b/crates/c-api/macros/src/lib.rs
@@ -96,7 +96,7 @@ pub fn declare_ref(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 
         #[no_mangle]
         pub extern fn #as_ref(a: &#ty) -> Box<crate::wasm_ref_t> {
-            let r = a.externref();
+            let r = Some(a.externref());
             Box::new(crate::wasm_ref_t { r })
         }
 
diff --git a/crates/c-api/src/engine.rs b/crates/c-api/src/engine.rs
index 843c261ea6..aad34312e6 100644
--- a/crates/c-api/src/engine.rs
+++ b/crates/c-api/src/engine.rs
@@ -1,10 +1,10 @@
 use crate::wasm_config_t;
-use wasmtime::{Engine, HostRef};
+use wasmtime::Engine;
 
 #[repr(C)]
 #[derive(Clone)]
 pub struct wasm_engine_t {
-    pub(crate) engine: HostRef<Engine>,
+    pub(crate) engine: Engine,
 }
 
 wasmtime_c_api_macros::declare_own!(wasm_engine_t);
@@ -22,7 +22,7 @@ pub extern "C" fn wasm_engine_new() -> Box<wasm_engine_t> {
     drop(env_logger::try_init());
 
     Box::new(wasm_engine_t {
-        engine: HostRef::new(Engine::default()),
+        engine: Engine::default(),
     })
 }
 
@@ -30,6 +30,6 @@ pub extern "C" fn wasm_engine_new() -> Box<wasm_engine_t> {
 pub extern "C" fn wasm_engine_new_with_config(c: Box<wasm_config_t>) -> Box<wasm_engine_t> {
     let config = c.config;
     Box::new(wasm_engine_t {
-        engine: HostRef::new(Engine::new(&config)),
+        engine: Engine::new(&config),
     })
 }
diff --git a/crates/c-api/src/error.rs b/crates/c-api/src/error.rs
index cbb84873df..3ea634b560 100644
--- a/crates/c-api/src/error.rs
+++ b/crates/c-api/src/error.rs
@@ -1,6 +1,6 @@
 use crate::{wasm_name_t, wasm_trap_t};
 use anyhow::{anyhow, Error, Result};
-use wasmtime::Trap;
+use wasmtime::{Store, Trap};
 
 #[repr(C)]
 pub struct wasmtime_error_t {
@@ -10,8 +10,8 @@ pub struct wasmtime_error_t {
 wasmtime_c_api_macros::declare_own!(wasmtime_error_t);
 
 impl wasmtime_error_t {
-    pub(crate) fn to_trap(self) -> Box<wasm_trap_t> {
-        Box::new(wasm_trap_t::new(Trap::from(self.error)))
+    pub(crate) fn to_trap(self, store: &Store) -> Box<wasm_trap_t> {
+        Box::new(wasm_trap_t::new(store, Trap::from(self.error)))
     }
 }
 
diff --git a/crates/c-api/src/extern.rs b/crates/c-api/src/extern.rs
index 025f233493..4a71807cd9 100644
--- a/crates/c-api/src/extern.rs
+++ b/crates/c-api/src/extern.rs
@@ -18,12 +18,12 @@ pub(crate) enum ExternHost {
 }
 
 impl wasm_extern_t {
-    fn externref(&self) -> wasmtime::ExternRef {
+    pub(crate) fn externref(&self) -> wasmtime::ExternRef {
         match &self.which {
-            ExternHost::Func(f) => f.externref(),
-            ExternHost::Global(f) => f.externref(),
-            ExternHost::Memory(f) => f.externref(),
-            ExternHost::Table(f) => f.externref(),
+            ExternHost::Func(f) => f.clone().into(),
+            ExternHost::Global(f) => f.clone().into(),
+            ExternHost::Memory(f) => f.clone().into(),
+            ExternHost::Table(f) => f.clone().into(),
         }
     }
 }
diff --git a/crates/c-api/src/func.rs b/crates/c-api/src/func.rs
index 0d3e3d10c8..855770dff3 100644
--- a/crates/c-api/src/func.rs
+++ b/crates/c-api/src/func.rs
@@ -71,7 +71,7 @@ impl wasm_func_t {
     }
 
     fn externref(&self) -> wasmtime::ExternRef {
-        self.func().externref()
+        self.func().clone().into()
     }
 }
 
@@ -90,7 +90,7 @@ fn create_function(
     ty: &wasm_functype_t,
     func: impl Fn(Caller<'_>, *const wasm_val_t, *mut wasm_val_t) -> Option<Box<wasm_trap_t>> + 'static,
 ) -> Box<wasm_func_t> {
-    let store = &store.store.borrow();
+    let store = &store.store;
     let ty = ty.ty().ty.clone();
     let func = Func::new(store, ty, move |caller, params, results| {
         let params = params
@@ -107,7 +107,7 @@ fn create_function(
         }
         Ok(())
     });
-    Box::new(HostRef::new(func).into())
+    Box::new(HostRef::new(store, func).into())
 }
 
 #[no_mangle]
@@ -182,7 +182,7 @@ pub unsafe extern "C" fn wasm_func_call(
         &mut trap,
     );
     match error {
-        Some(err) => Box::into_raw(err.to_trap()),
+        Some(err) => Box::into_raw(err.to_trap(&wasm_func.ext.externref().store().unwrap())),
         None => trap,
     }
 }
@@ -210,6 +210,7 @@ fn _wasmtime_func_call(
     results: &mut [wasm_val_t],
     trap_ptr: &mut *mut wasm_trap_t,
 ) -> Option<Box<wasmtime_error_t>> {
+    let store = &func.ext.externref().store().unwrap();
     let func = func.func().borrow();
     if results.len() != func.result_arity() {
         return Some(Box::new(anyhow!("wrong number of results provided").into()));
@@ -230,7 +231,7 @@ fn _wasmtime_func_call(
         }
         Ok(Err(trap)) => match trap.downcast::<Trap>() {
             Ok(trap) => {
-                *trap_ptr = Box::into_raw(Box::new(wasm_trap_t::new(trap)));
+                *trap_ptr = Box::into_raw(Box::new(wasm_trap_t::new(store, trap)));
                 None
             }
             Err(err) => Some(Box::new(err.into())),
@@ -243,7 +244,7 @@ fn _wasmtime_func_call(
             } else {
                 Trap::new("rust panic happened")
             };
-            let trap = Box::new(wasm_trap_t::new(trap));
+            let trap = Box::new(wasm_trap_t::new(store, trap));
             *trap_ptr = Box::into_raw(trap);
             None
         }
@@ -277,11 +278,12 @@ pub unsafe extern "C" fn wasmtime_caller_export_get(
 ) -> Option<Box<wasm_extern_t>> {
     let name = str::from_utf8(name.as_slice()).ok()?;
     let export = caller.caller.get_export(name)?;
+    let store = caller.caller.store();
     let which = match export {
-        Extern::Func(f) => ExternHost::Func(HostRef::new(f)),
-        Extern::Global(g) => ExternHost::Global(HostRef::new(g)),
-        Extern::Memory(m) => ExternHost::Memory(HostRef::new(m)),
-        Extern::Table(t) => ExternHost::Table(HostRef::new(t)),
+        Extern::Func(f) => ExternHost::Func(HostRef::new(&store, f)),
+        Extern::Global(g) => ExternHost::Global(HostRef::new(&store, g)),
+        Extern::Memory(m) => ExternHost::Memory(HostRef::new(&store, m)),
+        Extern::Table(t) => ExternHost::Table(HostRef::new(&store, t)),
     };
     Some(Box::new(wasm_extern_t { which }))
 }
diff --git a/crates/c-api/src/global.rs b/crates/c-api/src/global.rs
index b7ef6ebd7b..29e9477fa6 100644
--- a/crates/c-api/src/global.rs
+++ b/crates/c-api/src/global.rs
@@ -27,7 +27,7 @@ impl wasm_global_t {
     }
 
     fn externref(&self) -> wasmtime::ExternRef {
-        self.global().externref()
+        self.global().clone().into()
     }
 }
 
@@ -54,11 +54,11 @@ pub extern "C" fn wasmtime_global_new(
     val: &wasm_val_t,
     ret: &mut *mut wasm_global_t,
 ) -> Option<Box<wasmtime_error_t>> {
-    let global = Global::new(&store.store.borrow(), gt.ty().ty.clone(), val.val());
+    let global = Global::new(&store.store, gt.ty().ty.clone(), val.val());
     handle_result(global, |global| {
         *ret = Box::into_raw(Box::new(wasm_global_t {
             ext: wasm_extern_t {
-                which: ExternHost::Global(HostRef::new(global)),
+                which: ExternHost::Global(HostRef::new(&store.store, global)),
             },
         }));
     })
diff --git a/crates/c-api/src/instance.rs b/crates/c-api/src/instance.rs
index 6d528530d6..a833f462eb 100644
--- a/crates/c-api/src/instance.rs
+++ b/crates/c-api/src/instance.rs
@@ -16,14 +16,15 @@ wasmtime_c_api_macros::declare_ref!(wasm_instance_t);
 
 impl wasm_instance_t {
     pub(crate) fn new(instance: Instance) -> wasm_instance_t {
+        let store = instance.store().clone();
         wasm_instance_t {
-            instance: HostRef::new(instance),
+            instance: HostRef::new(&store, instance),
             exports_cache: RefCell::new(None),
         }
     }
 
     fn externref(&self) -> wasmtime::ExternRef {
-        self.instance.externref()
+        self.instance.clone().into()
     }
 }
 
@@ -34,12 +35,12 @@ pub unsafe extern "C" fn wasm_instance_new(
     imports: *const Box<wasm_extern_t>,
     result: Option<&mut *mut wasm_trap_t>,
 ) -> Option<Box<wasm_instance_t>> {
-    let store = &store.store.borrow();
+    let store = &store.store;
     let module = &wasm_module.module.borrow();
     if !Store::same(&store, module.store()) {
         if let Some(result) = result {
             let trap = Trap::new("wasm_store_t must match store in wasm_module_t");
-            let trap = Box::new(wasm_trap_t::new(trap));
+            let trap = Box::new(wasm_trap_t::new(store, trap));
             *result = Box::into_raw(trap);
         }
         return None;
@@ -58,7 +59,7 @@ pub unsafe extern "C" fn wasm_instance_new(
             assert!(trap.is_null());
             assert!(instance.is_null());
             if let Some(result) = result {
-                *result = Box::into_raw(err.to_trap());
+                *result = Box::into_raw(err.to_trap(store));
             }
             None
         }
@@ -111,10 +112,16 @@ fn _wasmtime_instance_new(
         })
         .collect::<Vec<_>>();
     let module = &module.module.borrow();
-    handle_instantiate(Instance::new(module, &imports), instance_ptr, trap_ptr)
+    handle_instantiate(
+        module.store(),
+        Instance::new(module, &imports),
+        instance_ptr,
+        trap_ptr,
+    )
 }
 
 pub fn handle_instantiate(
+    store: &Store,
     instance: Result<Instance>,
     instance_ptr: &mut *mut wasm_instance_t,
     trap_ptr: &mut *mut wasm_trap_t,
@@ -130,7 +137,7 @@ pub fn handle_instantiate(
         }
         Err(e) => match e.downcast::<Trap>() {
             Ok(trap) => {
-                write(trap_ptr, wasm_trap_t::new(trap));
+                write(trap_ptr, wasm_trap_t::new(store, trap));
                 None
             }
             Err(e) => Some(Box::new(e.into())),
@@ -146,10 +153,10 @@ pub extern "C" fn wasm_instance_exports(instance: &wasm_instance_t, out: &mut wa
         instance
             .exports()
             .map(|e| match e.into_extern() {
-                Extern::Func(f) => ExternHost::Func(HostRef::new(f)),
-                Extern::Global(f) => ExternHost::Global(HostRef::new(f)),
-                Extern::Memory(f) => ExternHost::Memory(HostRef::new(f)),
-                Extern::Table(f) => ExternHost::Table(HostRef::new(f)),
+                Extern::Func(f) => ExternHost::Func(HostRef::new(instance.store(), f)),
+                Extern::Global(f) => ExternHost::Global(HostRef::new(instance.store(), f)),
+                Extern::Memory(f) => ExternHost::Memory(HostRef::new(instance.store(), f)),
+                Extern::Table(f) => ExternHost::Table(HostRef::new(instance.store(), f)),
             })
             .collect()
     });
diff --git a/crates/c-api/src/linker.rs b/crates/c-api/src/linker.rs
index 3578544ef2..24c565c383 100644
--- a/crates/c-api/src/linker.rs
+++ b/crates/c-api/src/linker.rs
@@ -12,7 +12,7 @@ pub struct wasmtime_linker_t {
 #[no_mangle]
 pub extern "C" fn wasmtime_linker_new(store: &wasm_store_t) -> Box<wasmtime_linker_t> {
     Box::new(wasmtime_linker_t {
-        linker: Linker::new(&store.store.borrow()),
+        linker: Linker::new(&store.store),
     })
 }
 
@@ -87,7 +87,7 @@ pub unsafe extern "C" fn wasmtime_linker_instantiate(
     trap_ptr: &mut *mut wasm_trap_t,
 ) -> Option<Box<wasmtime_error_t>> {
     let result = linker.linker.instantiate(&module.module.borrow());
-    super::instance::handle_instantiate(result, instance_ptr, trap_ptr)
+    super::instance::handle_instantiate(linker.linker.store(), result, instance_ptr, trap_ptr)
 }
 
 #[no_mangle]
@@ -116,6 +116,6 @@ pub unsafe extern "C" fn wasmtime_linker_get_default(
         Err(_) => return bad_utf8(),
     };
     handle_result(linker.get_default(name), |f| {
-        *func = Box::into_raw(Box::new(HostRef::new(f).into()))
+        *func = Box::into_raw(Box::new(HostRef::new(linker.store(), f).into()))
     })
 }
diff --git a/crates/c-api/src/memory.rs b/crates/c-api/src/memory.rs
index 48159b94ed..aa3e2e4db3 100644
--- a/crates/c-api/src/memory.rs
+++ b/crates/c-api/src/memory.rs
@@ -27,7 +27,7 @@ impl wasm_memory_t {
     }
 
     fn externref(&self) -> wasmtime::ExternRef {
-        self.memory().externref()
+        self.memory().clone().into()
     }
 }
 
@@ -36,7 +36,7 @@ pub extern "C" fn wasm_memory_new(
     store: &wasm_store_t,
     mt: &wasm_memorytype_t,
 ) -> Box<wasm_memory_t> {
-    let memory = HostRef::new(Memory::new(&store.store.borrow(), mt.ty().ty.clone()));
+    let memory = HostRef::new(&store.store, Memory::new(&store.store, mt.ty().ty.clone()));
     Box::new(wasm_memory_t {
         ext: wasm_extern_t {
             which: ExternHost::Memory(memory),
diff --git a/crates/c-api/src/module.rs b/crates/c-api/src/module.rs
index 23c5eae364..2349e20bef 100644
--- a/crates/c-api/src/module.rs
+++ b/crates/c-api/src/module.rs
@@ -16,7 +16,7 @@ wasmtime_c_api_macros::declare_ref!(wasm_module_t);
 
 impl wasm_module_t {
     fn externref(&self) -> wasmtime::ExternRef {
-        self.module.externref()
+        self.module.clone().into()
     }
 }
 
@@ -42,7 +42,7 @@ pub extern "C" fn wasmtime_module_new(
     ret: &mut *mut wasm_module_t,
 ) -> Option<Box<wasmtime_error_t>> {
     let binary = binary.as_slice();
-    let store = &store.store.borrow();
+    let store = &store.store;
     handle_result(Module::from_binary(store, binary), |module| {
         let imports = module
             .imports()
@@ -53,7 +53,7 @@ pub extern "C" fn wasmtime_module_new(
             .map(|e| wasm_exporttype_t::new(e.name().to_owned(), e.ty()))
             .collect::<Vec<_>>();
         let module = Box::new(wasm_module_t {
-            module: HostRef::new(module),
+            module: HostRef::new(store, module),
             imports,
             exports,
         });
@@ -72,7 +72,7 @@ pub extern "C" fn wasmtime_module_validate(
     binary: &wasm_byte_vec_t,
 ) -> Option<Box<wasmtime_error_t>> {
     let binary = binary.as_slice();
-    let store = &store.store.borrow();
+    let store = &store.store;
     handle_result(Module::validate(store, binary), |()| {})
 }
 
diff --git a/crates/c-api/src/ref.rs b/crates/c-api/src/ref.rs
index 00f93865ce..5e14c51c38 100644
--- a/crates/c-api/src/ref.rs
+++ b/crates/c-api/src/ref.rs
@@ -5,7 +5,7 @@ use wasmtime::ExternRef;
 #[repr(C)]
 #[derive(Clone)]
 pub struct wasm_ref_t {
-    pub(crate) r: ExternRef,
+    pub(crate) r: Option<ExternRef>,
 }
 
 wasmtime_c_api_macros::declare_own!(wasm_ref_t);
@@ -17,7 +17,11 @@ pub extern "C" fn wasm_ref_copy(r: &wasm_ref_t) -> Box<wasm_ref_t> {
 
 #[no_mangle]
 pub extern "C" fn wasm_ref_same(a: &wasm_ref_t, b: &wasm_ref_t) -> bool {
-    a.r.ptr_eq(&b.r)
+    match (a.r.as_ref(), b.r.as_ref()) {
+        (Some(a), Some(b)) => a.ptr_eq(b),
+        (None, None) => true,
+        _ => false,
+    }
 }
 
 pub(crate) fn get_host_info(r: &ExternRef) -> *mut c_void {
@@ -25,6 +29,7 @@ pub(crate) fn get_host_info(r: &ExternRef) -> *mut c_void {
         Some(info) => info,
         None => return std::ptr::null_mut(),
     };
+    let host_info = host_info.borrow();
     match host_info.downcast_ref::<HostInfoState>() {
         Some(state) => state.info,
         None => std::ptr::null_mut(),
@@ -33,7 +38,8 @@ pub(crate) fn get_host_info(r: &ExternRef) -> *mut c_void {
 
 #[no_mangle]
 pub extern "C" fn wasm_ref_get_host_info(a: &wasm_ref_t) -> *mut c_void {
-    get_host_info(&a.r)
+    a.r.as_ref()
+        .map_or(std::ptr::null_mut(), |r| get_host_info(r))
 }
 
 pub(crate) fn set_host_info(
@@ -51,7 +57,7 @@ pub(crate) fn set_host_info(
 
 #[no_mangle]
 pub extern "C" fn wasm_ref_set_host_info(a: &wasm_ref_t, info: *mut c_void) {
-    set_host_info(&a.r, info, None)
+    a.r.as_ref().map(|r| set_host_info(r, info, None));
 }
 
 #[no_mangle]
@@ -60,5 +66,5 @@ pub extern "C" fn wasm_ref_set_host_info_with_finalizer(
     info: *mut c_void,
     finalizer: Option<extern "C" fn(*mut c_void)>,
 ) {
-    set_host_info(&a.r, info, finalizer)
+    a.r.as_ref().map(|r| set_host_info(r, info, finalizer));
 }
diff --git a/crates/c-api/src/store.rs b/crates/c-api/src/store.rs
index a2a5b1c25b..625b3831ea 100644
--- a/crates/c-api/src/store.rs
+++ b/crates/c-api/src/store.rs
@@ -1,10 +1,10 @@
 use crate::wasm_engine_t;
-use wasmtime::{HostRef, InterruptHandle, Store};
+use wasmtime::{InterruptHandle, Store};
 
 #[repr(C)]
 #[derive(Clone)]
 pub struct wasm_store_t {
-    pub(crate) store: HostRef<Store>,
+    pub(crate) store: Store,
 }
 
 wasmtime_c_api_macros::declare_own!(wasm_store_t);
@@ -13,7 +13,7 @@ wasmtime_c_api_macros::declare_own!(wasm_store_t);
 pub extern "C" fn wasm_store_new(engine: &wasm_engine_t) -> Box<wasm_store_t> {
     let engine = &engine.engine;
     Box::new(wasm_store_t {
-        store: HostRef::new(Store::new(&engine.borrow())),
+        store: Store::new(&engine),
     })
 }
 
@@ -29,7 +29,7 @@ pub extern "C" fn wasmtime_interrupt_handle_new(
     store: &wasm_store_t,
 ) -> Option<Box<wasmtime_interrupt_handle_t>> {
     Some(Box::new(wasmtime_interrupt_handle_t {
-        handle: store.store.borrow().interrupt_handle().ok()?,
+        handle: store.store.interrupt_handle().ok()?,
     }))
 }
 
diff --git a/crates/c-api/src/table.rs b/crates/c-api/src/table.rs
index 16626acf7b..e49daddef8 100644
--- a/crates/c-api/src/table.rs
+++ b/crates/c-api/src/table.rs
@@ -1,7 +1,7 @@
 use crate::{handle_result, wasm_func_t, wasm_ref_t, wasmtime_error_t};
 use crate::{wasm_extern_t, wasm_store_t, wasm_tabletype_t, ExternHost};
 use std::ptr;
-use wasmtime::{ExternRef, HostRef, Table, Val};
+use wasmtime::{HostRef, Table, Val};
 
 #[derive(Clone)]
 #[repr(transparent)]
@@ -29,7 +29,7 @@ impl wasm_table_t {
     }
 
     fn externref(&self) -> wasmtime::ExternRef {
-        self.table().externref()
+        self.table().clone().into()
     }
 }
 
@@ -41,12 +41,12 @@ pub extern "C" fn wasm_table_new(
 ) -> Option<Box<wasm_table_t>> {
     let init: Val = match init {
         Some(init) => init.r.into(),
-        None => Val::ExternRef(ExternRef::Null),
+        None => Val::ExternRef(None),
     };
-    let table = Table::new(&store.store.borrow(), tt.ty().ty.clone(), init).ok()?;
+    let table = Table::new(&store.store, tt.ty().ty.clone(), init).ok()?;
     Some(Box::new(wasm_table_t {
         ext: wasm_extern_t {
-            which: ExternHost::Table(HostRef::new(table)),
+            which: ExternHost::Table(HostRef::new(&store.store, table)),
         },
     }))
 }
@@ -60,14 +60,14 @@ pub extern "C" fn wasmtime_funcref_table_new(
 ) -> Option<Box<wasmtime_error_t>> {
     let init: Val = match init {
         Some(val) => Val::FuncRef(val.func().borrow().clone()),
-        None => Val::ExternRef(ExternRef::Null),
+        None => Val::ExternRef(None),
     };
     handle_result(
-        Table::new(&store.store.borrow(), tt.ty().ty.clone(), init),
+        Table::new(&store.store, tt.ty().ty.clone(), init),
         |table| {
             *out = Box::into_raw(Box::new(wasm_table_t {
                 ext: wasm_extern_t {
-                    which: ExternHost::Table(HostRef::new(table)),
+                    which: ExternHost::Table(HostRef::new(&store.store, table)),
                 },
             }));
         },
@@ -84,7 +84,7 @@ pub extern "C" fn wasm_table_type(t: &wasm_table_t) -> Box<wasm_tabletype_t> {
 pub extern "C" fn wasm_table_get(t: &wasm_table_t, index: wasm_table_size_t) -> *mut wasm_ref_t {
     match t.table().borrow().get(index) {
         Some(val) => into_funcref(val),
-        None => into_funcref(Val::ExternRef(ExternRef::Null)),
+        None => into_funcref(Val::ExternRef(None)),
     }
 }
 
@@ -98,8 +98,14 @@ pub extern "C" fn wasmtime_funcref_table_get(
         Some(val) => {
             *ptr = match val {
                 // TODO: what do do about creating new `HostRef` handles here?
-                Val::FuncRef(f) => Box::into_raw(Box::new(HostRef::new(f).into())),
-                Val::ExternRef(ExternRef::Null) => ptr::null_mut(),
+                Val::FuncRef(f) => {
+                    let store = match t.table().as_ref().store() {
+                        None => return false,
+                        Some(store) => store,
+                    };
+                    Box::into_raw(Box::new(HostRef::new(&store, f).into()))
+                }
+                Val::ExternRef(None) => ptr::null_mut(),
                 _ => return false,
             };
         }
@@ -127,13 +133,13 @@ pub extern "C" fn wasmtime_funcref_table_set(
 ) -> Option<Box<wasmtime_error_t>> {
     let val = match val {
         Some(val) => Val::FuncRef(val.func().borrow().clone()),
-        None => Val::ExternRef(ExternRef::Null),
+        None => Val::ExternRef(None),
     };
     handle_result(t.table().borrow().set(index, val), |()| {})
 }
 
 fn into_funcref(val: Val) -> *mut wasm_ref_t {
-    if let Val::ExternRef(ExternRef::Null) = val {
+    if let Val::ExternRef(None) = val {
         return ptr::null_mut();
     }
     let externref = match val.externref() {
@@ -148,7 +154,7 @@ unsafe fn from_funcref(r: *mut wasm_ref_t) -> Val {
     if !r.is_null() {
         Box::from_raw(r).r.into()
     } else {
-        Val::ExternRef(ExternRef::Null)
+        Val::ExternRef(None)
     }
 }
 
@@ -176,7 +182,7 @@ pub extern "C" fn wasmtime_funcref_table_grow(
 ) -> Option<Box<wasmtime_error_t>> {
     let val = match init {
         Some(val) => Val::FuncRef(val.func().borrow().clone()),
-        None => Val::ExternRef(ExternRef::Null),
+        None => Val::ExternRef(None),
     };
     handle_result(t.table().borrow().grow(delta, val), |prev| {
         if let Some(ptr) = prev_size {
diff --git a/crates/c-api/src/trap.rs b/crates/c-api/src/trap.rs
index 5f0cc2df98..c7a906e3eb 100644
--- a/crates/c-api/src/trap.rs
+++ b/crates/c-api/src/trap.rs
@@ -1,6 +1,6 @@
 use crate::{wasm_frame_vec_t, wasm_instance_t, wasm_name_t, wasm_store_t};
 use once_cell::unsync::OnceCell;
-use wasmtime::{HostRef, Trap};
+use wasmtime::{HostRef, Store, Trap};
 
 #[repr(C)]
 #[derive(Clone)]
@@ -11,14 +11,14 @@ pub struct wasm_trap_t {
 wasmtime_c_api_macros::declare_ref!(wasm_trap_t);
 
 impl wasm_trap_t {
-    pub(crate) fn new(trap: Trap) -> wasm_trap_t {
+    pub(crate) fn new(store: &Store, trap: Trap) -> wasm_trap_t {
         wasm_trap_t {
-            trap: HostRef::new(trap),
+            trap: HostRef::new(store, trap),
         }
     }
 
     fn externref(&self) -> wasmtime::ExternRef {
-        self.trap.externref()
+        self.trap.clone().into()
     }
 }
 
@@ -37,7 +37,7 @@ pub type wasm_message_t = wasm_name_t;
 
 #[no_mangle]
 pub extern "C" fn wasm_trap_new(
-    _store: &wasm_store_t,
+    store: &wasm_store_t,
     message: &wasm_message_t,
 ) -> Box<wasm_trap_t> {
     let message = message.as_slice();
@@ -46,7 +46,7 @@ pub extern "C" fn wasm_trap_new(
     }
     let message = String::from_utf8_lossy(&message[..message.len() - 1]);
     Box::new(wasm_trap_t {
-        trap: HostRef::new(Trap::new(message)),
+        trap: HostRef::new(&store.store, Trap::new(message)),
     })
 }
 
diff --git a/crates/c-api/src/wasi.rs b/crates/c-api/src/wasi.rs
index a3b3ef8e84..f1db5d6c6b 100644
--- a/crates/c-api/src/wasi.rs
+++ b/crates/c-api/src/wasi.rs
@@ -282,7 +282,7 @@ pub unsafe extern "C" fn wasi_instance_new(
     config: Box<wasi_config_t>,
     trap: &mut *mut wasm_trap_t,
 ) -> Option<Box<wasi_instance_t>> {
-    let store = &store.store.borrow();
+    let store = &store.store;
 
     let result = match CStr::from_ptr(name).to_str().unwrap_or("") {
         "wasi_snapshot_preview1" => create_preview1_instance(store, *config),
@@ -297,7 +297,7 @@ pub unsafe extern "C" fn wasi_instance_new(
         })),
         Err(e) => {
             *trap = Box::into_raw(Box::new(wasm_trap_t {
-                trap: HostRef::new(Trap::new(e)),
+                trap: HostRef::new(store, Trap::new(e)),
             }));
 
             None
@@ -335,13 +335,14 @@ pub extern "C" fn wasi_instance_bind_import<'a>(
     if &export.ty() != import.ty.func()? {
         return None;
     }
+    let store = export.store();
 
     let entry = instance
         .export_cache
         .entry(name.to_string())
         .or_insert_with(|| {
             Box::new(wasm_extern_t {
-                which: ExternHost::Func(HostRef::new(export.clone())),
+                which: ExternHost::Func(HostRef::new(store, export.clone())),
             })
         });
     Some(entry)
diff --git a/crates/environ/src/cranelift.rs b/crates/environ/src/cranelift.rs
index e8e05c2438..d7d0146a6e 100644
--- a/crates/environ/src/cranelift.rs
+++ b/crates/environ/src/cranelift.rs
@@ -303,7 +303,7 @@ fn compile(env: CompileEnv<'_>) -> Result<ModuleCacheDataTupleType, CompileError
             let func_index = env.local.func_index(*i);
             let mut context = Context::new();
             context.func.name = get_func_name(func_index);
-            context.func.signature = env.local.func_signature(func_index).clone();
+            context.func.signature = env.local.native_func_signature(func_index).clone();
             if env.tunables.debug_info {
                 context.func.collect_debug_info();
             }
diff --git a/crates/environ/src/data_structures.rs b/crates/environ/src/data_structures.rs
index e12768a4cd..30d00d1d0e 100755
--- a/crates/environ/src/data_structures.rs
+++ b/crates/environ/src/data_structures.rs
@@ -24,6 +24,6 @@ pub mod wasm {
     pub use cranelift_wasm::{
         get_vmctx_value_label, DataIndex, DefinedFuncIndex, DefinedGlobalIndex, DefinedMemoryIndex,
         DefinedTableIndex, ElemIndex, FuncIndex, Global, GlobalIndex, GlobalInit, Memory,
-        MemoryIndex, SignatureIndex, Table, TableElementType, TableIndex,
+        MemoryIndex, SignatureIndex, Table, TableElementType, TableIndex, WasmFuncType, WasmType,
     };
 }
diff --git a/crates/environ/src/func_environ.rs b/crates/environ/src/func_environ.rs
index 6ca501eb9a..52e4fbb64a 100644
--- a/crates/environ/src/func_environ.rs
+++ b/crates/environ/src/func_environ.rs
@@ -549,7 +549,7 @@ impl lightbeam::ModuleContext for FuncEnvironment<'_> {
     }
 
     fn signature(&self, index: u32) -> &Self::Signature {
-        &self.module.signatures[SignatureIndex::from_u32(index)]
+        &self.module.signatures[SignatureIndex::from_u32(index)].1
     }
 
     fn defined_table_index(&self, table_index: u32) -> Option<u32> {
@@ -658,6 +658,13 @@ impl<'module_environment> TargetEnvironment for FuncEnvironment<'module_environm
     fn target_config(&self) -> TargetFrontendConfig {
         self.target_config
     }
+
+    fn reference_type(&self) -> ir::Type {
+        // For now, the only reference types we support are `externref`, which
+        // don't require tracing GC and stack maps. So we just use the target's
+        // pointer type. This will have to change once we move to tracing GC.
+        self.pointer_type()
+    }
 }
 
 impl<'module_environment> cranelift_wasm::FuncEnvironment for FuncEnvironment<'module_environment> {
@@ -915,7 +922,7 @@ impl<'module_environment> cranelift_wasm::FuncEnvironment for FuncEnvironment<'m
         func: &mut ir::Function,
         index: SignatureIndex,
     ) -> WasmResult<ir::SigRef> {
-        Ok(func.import_signature(self.module.signatures[index].clone()))
+        Ok(func.import_signature(self.module.signatures[index].1.clone()))
     }
 
     fn make_direct_func(
@@ -923,7 +930,7 @@ impl<'module_environment> cranelift_wasm::FuncEnvironment for FuncEnvironment<'m
         func: &mut ir::Function,
         index: FuncIndex,
     ) -> WasmResult<ir::FuncRef> {
-        let sig = self.module.func_signature(index);
+        let sig = self.module.native_func_signature(index);
         let signature = func.import_signature(sig.clone());
         let name = get_func_name(index);
         Ok(func.import_function(ir::ExtFuncData {
diff --git a/crates/environ/src/module.rs b/crates/environ/src/module.rs
index 9a079e157b..280210cfa4 100644
--- a/crates/environ/src/module.rs
+++ b/crates/environ/src/module.rs
@@ -7,7 +7,7 @@ use cranelift_entity::{EntityRef, PrimaryMap};
 use cranelift_wasm::{
     DataIndex, DefinedFuncIndex, DefinedGlobalIndex, DefinedMemoryIndex, DefinedTableIndex,
     ElemIndex, FuncIndex, Global, GlobalIndex, Memory, MemoryIndex, SignatureIndex, Table,
-    TableIndex,
+    TableIndex, WasmFuncType,
 };
 use indexmap::IndexMap;
 use more_asserts::assert_ge;
@@ -181,7 +181,7 @@ pub struct Module {
 #[derive(Debug, Hash)]
 pub struct ModuleLocal {
     /// Unprocessed signatures exactly as provided by `declare_signature()`.
-    pub signatures: PrimaryMap<SignatureIndex, ir::Signature>,
+    pub signatures: PrimaryMap<SignatureIndex, (WasmFuncType, ir::Signature)>,
 
     /// Number of imported functions in the module.
     pub num_imported_funcs: usize,
@@ -332,8 +332,15 @@ impl ModuleLocal {
         index.index() < self.num_imported_globals
     }
 
-    /// Convenience method for looking up the signature of a function.
-    pub fn func_signature(&self, func_index: FuncIndex) -> &ir::Signature {
-        &self.signatures[self.functions[func_index]]
+    /// Convenience method for looking up the native signature of a compiled
+    /// Wasm function.
+    pub fn native_func_signature(&self, func_index: FuncIndex) -> &ir::Signature {
+        &self.signatures[self.functions[func_index]].1
+    }
+
+    /// Convenience method for looking up the original Wasm signature of a
+    /// function.
+    pub fn wasm_func_type(&self, func_index: FuncIndex) -> &WasmFuncType {
+        &self.signatures[self.functions[func_index]].0
     }
 }
diff --git a/crates/environ/src/module_environ.rs b/crates/environ/src/module_environ.rs
index 9061775d66..7553215119 100644
--- a/crates/environ/src/module_environ.rs
+++ b/crates/environ/src/module_environ.rs
@@ -92,6 +92,13 @@ impl<'data> TargetEnvironment for ModuleEnvironment<'data> {
     fn target_config(&self) -> TargetFrontendConfig {
         self.result.target_config
     }
+
+    fn reference_type(&self) -> ir::Type {
+        // For now, the only reference types we support are `externref`, which
+        // don't require tracing GC and stack maps. So we just use the target's
+        // pointer type. This will have to change once we move to tracing GC.
+        self.pointer_type()
+    }
 }
 
 /// This trait is useful for `translate_module` because it tells how to translate
@@ -106,10 +113,14 @@ impl<'data> cranelift_wasm::ModuleEnvironment<'data> for ModuleEnvironment<'data
         Ok(())
     }
 
-    fn declare_signature(&mut self, _wasm: &WasmFuncType, sig: ir::Signature) -> WasmResult<()> {
+    fn declare_signature(&mut self, wasm: &WasmFuncType, sig: ir::Signature) -> WasmResult<()> {
         let sig = translate_signature(sig, self.pointer_type());
         // TODO: Deduplicate signatures.
-        self.result.module.local.signatures.push(sig);
+        self.result
+            .module
+            .local
+            .signatures
+            .push((wasm.clone(), sig));
         Ok(())
     }
 
diff --git a/crates/jit/src/compiler.rs b/crates/jit/src/compiler.rs
index 0bcef5f0fc..7ba94986a5 100644
--- a/crates/jit/src/compiler.rs
+++ b/crates/jit/src/compiler.rs
@@ -149,8 +149,10 @@ impl Compiler {
         let mut cx = FunctionBuilderContext::new();
         let mut trampolines = HashMap::new();
         let mut trampoline_relocations = HashMap::new();
-        for sig in translation.module.local.signatures.values() {
-            let index = self.signatures.register(sig);
+        for (wasm_func_ty, native_sig) in translation.module.local.signatures.values() {
+            let index = self
+                .signatures
+                .register(wasm_func_ty.clone(), native_sig.clone());
             if trampolines.contains_key(&index) {
                 continue;
             }
@@ -158,7 +160,7 @@ impl Compiler {
                 &*self.isa,
                 &mut self.code_memory,
                 &mut cx,
-                sig,
+                native_sig,
                 std::mem::size_of::<u128>(),
             )?;
             trampolines.insert(index, trampoline);
@@ -167,7 +169,7 @@ impl Compiler {
             // show up be sure to log it in case anyone's listening and there's
             // an accidental bug.
             if relocations.len() > 0 {
-                log::info!("relocations found in trampoline for {:?}", sig);
+                log::info!("relocations found in trampoline for {:?}", native_sig);
                 trampoline_relocations.insert(index, relocations);
             }
         }
diff --git a/crates/jit/src/imports.rs b/crates/jit/src/imports.rs
index d2ef3536fc..cf0f497e15 100644
--- a/crates/jit/src/imports.rs
+++ b/crates/jit/src/imports.rs
@@ -31,8 +31,8 @@ pub fn resolve_imports(
 
         match (import, &export) {
             (EntityIndex::Function(func_index), Some(Export::Function(f))) => {
-                let import_signature = module.local.func_signature(*func_index);
-                let signature = signatures.lookup(f.signature).unwrap();
+                let import_signature = module.local.native_func_signature(*func_index);
+                let signature = signatures.lookup_native(f.signature).unwrap();
                 if signature != *import_signature {
                     // TODO: If the difference is in the calling convention,
                     // we could emit a wrapper function to fix it up.
diff --git a/crates/jit/src/instantiate.rs b/crates/jit/src/instantiate.rs
index e3f1a5eb96..d92a55fe3c 100644
--- a/crates/jit/src/instantiate.rs
+++ b/crates/jit/src/instantiate.rs
@@ -93,7 +93,7 @@ impl<'data> RawCompiledModule<'data> {
                 .local
                 .signatures
                 .values()
-                .map(|sig| signature_registry.register(sig))
+                .map(|(wasm, native)| signature_registry.register(wasm.clone(), native.clone()))
                 .collect::<PrimaryMap<_, _>>()
         };
 
diff --git a/crates/runtime/src/externref.rs b/crates/runtime/src/externref.rs
index f7f085fe67..9f2ea1e481 100644
--- a/crates/runtime/src/externref.rs
+++ b/crates/runtime/src/externref.rs
@@ -57,6 +57,21 @@
 //! to hold everything satisfies its alignment. It also ensures that we don't
 //! need a ton of excess padding between the `VMExternData` and the value for
 //! values with large alignment.
+//!
+//! ## Reference Counting Protocol and Wasm Functions
+//!
+//! Currently, `VMExternRef`s passed into compiled Wasm functions have move
+//! semantics: the host code gives up ownership and does not decrement the
+//! reference count. Similarly, `VMExternRef`s returned from compiled Wasm
+//! functions also have move semantics: host code takes ownership and the
+//! reference count is not incremented.
+//!
+//! This works well when a reference is passed into Wasm and then passed back
+//! out again. However, if a reference is passed into Wasm, but not passed back
+//! out, then the reference is leaked. This is only a temporary state, and
+//! follow up work will leverage stack maps to fix this issue. Follow
+//! https://github.com/bytecodealliance/wasmtime/issues/929 to keep an eye on
+//! this.
 
 use std::alloc::Layout;
 use std::any::Any;
diff --git a/crates/runtime/src/sig_registry.rs b/crates/runtime/src/sig_registry.rs
index 7ad66149ac..7ea07ddf48 100644
--- a/crates/runtime/src/sig_registry.rs
+++ b/crates/runtime/src/sig_registry.rs
@@ -2,11 +2,11 @@
 //! signature checking.
 
 use crate::vmcontext::VMSharedSignatureIndex;
-use more_asserts::{assert_lt, debug_assert_lt};
-use std::collections::{hash_map, HashMap};
+use more_asserts::assert_lt;
+use std::collections::HashMap;
 use std::convert::TryFrom;
 use std::sync::RwLock;
-use wasmtime_environ::ir;
+use wasmtime_environ::{ir, wasm::WasmFuncType};
 
 /// WebAssembly requires that the caller and callee signatures in an indirect
 /// call must match. To implement this efficiently, keep a registry of all
@@ -24,8 +24,13 @@ pub struct SignatureRegistry {
 
 #[derive(Debug, Default)]
 struct Inner {
-    signature2index: HashMap<ir::Signature, VMSharedSignatureIndex>,
-    index2signature: HashMap<VMSharedSignatureIndex, ir::Signature>,
+    wasm2index: HashMap<WasmFuncType, VMSharedSignatureIndex>,
+
+    // Maps the index to the original Wasm signature.
+    index2wasm: HashMap<VMSharedSignatureIndex, WasmFuncType>,
+
+    // Maps the index to the native signature.
+    index2native: HashMap<VMSharedSignatureIndex, ir::Signature>,
 }
 
 impl SignatureRegistry {
@@ -37,37 +42,42 @@ impl SignatureRegistry {
     }
 
     /// Register a signature and return its unique index.
-    pub fn register(&self, sig: &ir::Signature) -> VMSharedSignatureIndex {
-        let mut inner = self.inner.write().unwrap();
-        let len = inner.signature2index.len();
-        match inner.signature2index.entry(sig.clone()) {
-            hash_map::Entry::Occupied(entry) => *entry.get(),
-            hash_map::Entry::Vacant(entry) => {
-                // Keep `signature_hash` len under 2**32 -- VMSharedSignatureIndex::new(std::u32::MAX)
-                // is reserved for VMSharedSignatureIndex::default().
-                debug_assert_lt!(
-                    len,
-                    std::u32::MAX as usize,
-                    "Invariant check: signature_hash.len() < std::u32::MAX"
-                );
-                let sig_id = VMSharedSignatureIndex::new(u32::try_from(len).unwrap());
-                entry.insert(sig_id);
-                inner.index2signature.insert(sig_id, sig.clone());
-                sig_id
-            }
-        }
+    pub fn register(&self, wasm: WasmFuncType, native: ir::Signature) -> VMSharedSignatureIndex {
+        let Inner {
+            wasm2index,
+            index2wasm,
+            index2native,
+        } = &mut *self.inner.write().unwrap();
+        let len = wasm2index.len();
+
+        *wasm2index.entry(wasm.clone()).or_insert_with(|| {
+            // Keep `signature_hash` len under 2**32 -- VMSharedSignatureIndex::new(std::u32::MAX)
+            // is reserved for VMSharedSignatureIndex::default().
+            assert_lt!(
+                len,
+                std::u32::MAX as usize,
+                "Invariant check: signature_hash.len() < std::u32::MAX"
+            );
+            let index = VMSharedSignatureIndex::new(u32::try_from(len).unwrap());
+            index2wasm.insert(index, wasm);
+            index2native.insert(index, native);
+            index
+        })
     }
 
-    /// Looks up a shared signature index within this registry.
+    /// Looks up a shared native signature within this registry.
     ///
     /// Note that for this operation to be semantically correct the `idx` must
     /// have previously come from a call to `register` of this same object.
-    pub fn lookup(&self, idx: VMSharedSignatureIndex) -> Option<ir::Signature> {
-        self.inner
-            .read()
-            .unwrap()
-            .index2signature
-            .get(&idx)
-            .cloned()
+    pub fn lookup_native(&self, idx: VMSharedSignatureIndex) -> Option<ir::Signature> {
+        self.inner.read().unwrap().index2native.get(&idx).cloned()
+    }
+
+    /// Looks up a shared Wasm signature within this registry.
+    ///
+    /// Note that for this operation to be semantically correct the `idx` must
+    /// have previously come from a call to `register` of this same object.
+    pub fn lookup_wasm(&self, idx: VMSharedSignatureIndex) -> Option<WasmFuncType> {
+        self.inner.read().unwrap().index2wasm.get(&idx).cloned()
     }
 }
diff --git a/crates/wasmtime/src/func.rs b/crates/wasmtime/src/func.rs
index 70bf2843bc..febd02b76e 100644
--- a/crates/wasmtime/src/func.rs
+++ b/crates/wasmtime/src/func.rs
@@ -244,9 +244,10 @@ impl Func {
             // number of arguments and the right types of arguments. As a result
             // we should be able to safely run through them all and read them.
             let mut args = Vec::with_capacity(ty_clone.params().len());
+            let store = Store::upgrade(&store_weak).unwrap();
             for (i, ty) in ty_clone.params().iter().enumerate() {
                 unsafe {
-                    args.push(Val::read_value_from(values_vec.add(i), ty));
+                    args.push(Val::read_value_from(&store, values_vec.add(i), ty));
                 }
             }
             let mut returns = vec![Val::null(); ty_clone.results().len()];
@@ -483,25 +484,25 @@ impl Func {
             .store
             .compiler()
             .signatures()
-            .lookup(self.export.signature)
+            .lookup_wasm(self.export.signature)
             .expect("failed to lookup signature");
 
         // This is only called with `Export::Function`, and since it's coming
         // from wasmtime_runtime itself we should support all the types coming
         // out of it, so assert such here.
-        FuncType::from_wasmtime_signature(&sig).expect("core wasm signature should be supported")
+        FuncType::from_wasm_func_type(&sig).expect("core wasm signature should be supported")
     }
 
     /// Returns the number of parameters that this function takes.
     pub fn param_arity(&self) -> usize {
-        let sig = self
-            .instance
+        self.instance
             .store
             .compiler()
             .signatures()
-            .lookup(self.export.signature)
-            .expect("failed to lookup signature");
-        sig.params.len() - 2 // skip the two vmctx leading parameters
+            .lookup_wasm(self.export.signature)
+            .expect("failed to lookup signature")
+            .params
+            .len()
     }
 
     /// Returns the number of results this function produces.
@@ -511,7 +512,7 @@ impl Func {
             .store
             .compiler()
             .signatures()
-            .lookup(self.export.signature)
+            .lookup_wasm(self.export.signature)
             .expect("failed to lookup signature");
         sig.returns.len()
     }
@@ -546,7 +547,11 @@ impl Func {
         let param_tys = my_ty.params().iter();
         for ((arg, slot), ty) in params.iter().zip(&mut values_vec).zip(param_tys) {
             if arg.ty() != *ty {
-                bail!("argument type mismatch");
+                bail!(
+                    "argument type mismatch: found {} but expected {}",
+                    arg.ty(),
+                    ty
+                );
             }
             if !arg.comes_from_same_store(&self.instance.store) {
                 bail!("cross-`Store` values are not currently supported");
@@ -571,7 +576,7 @@ impl Func {
         for (index, ty) in my_ty.results().iter().enumerate() {
             unsafe {
                 let ptr = values_vec.as_ptr().add(index);
-                results.push(Val::read_value_from(ptr, ty));
+                results.push(Val::read_value_from(&self.instance.store, ptr, ty));
             }
         }
 
@@ -722,7 +727,10 @@ impl Func {
         (get15, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15)
     }
 
-    pub(crate) fn store(&self) -> &Store {
+    // This should be `pub(crate)` but the C API happens to need it in one
+    // place.
+    #[doc(hidden)]
+    pub fn store(&self) -> &Store {
         &self.instance.store
     }
 }
@@ -1038,6 +1046,12 @@ impl Caller<'_> {
             Some(Extern::Memory(mem))
         }
     }
+
+    /// Get a handle to this caller's store.
+    pub fn store(&self) -> Store {
+        // See comment above the `store` member for why this unwrap is OK.
+        Store::upgrade(&self.store).unwrap()
+    }
 }
 
 macro_rules! impl_into_func {
diff --git a/crates/wasmtime/src/ref.rs b/crates/wasmtime/src/ref.rs
old mode 100644
new mode 100755
index f78aaf0e9c..5c6cc540cb
--- a/crates/wasmtime/src/ref.rs
+++ b/crates/wasmtime/src/ref.rs
@@ -2,224 +2,182 @@
 
 use std::any::Any;
 use std::cell::{self, RefCell};
+use std::convert::TryFrom;
 use std::fmt;
+use std::marker::PhantomData;
 use std::rc::{Rc, Weak};
-
-trait InternalRefBase: Any {
-    fn as_any(&self) -> &dyn Any;
-    fn host_info(&self) -> Option<cell::RefMut<Box<dyn Any>>>;
-    fn set_host_info(&self, info: Option<Box<dyn Any>>);
-    fn ptr_eq(&self, other: &dyn InternalRefBase) -> bool;
-}
-
-#[derive(Clone)]
-pub struct InternalRef(Rc<dyn InternalRefBase>);
-
-impl InternalRef {
-    pub fn is_ref<T: 'static>(&self) -> bool {
-        let r = self.0.as_any();
-        Any::is::<HostRef<T>>(r)
-    }
-    pub fn get_ref<T: 'static>(&self) -> HostRef<T> {
-        let r = self.0.as_any();
-        r.downcast_ref::<HostRef<T>>()
-            .expect("reference is not T type")
-            .clone()
-    }
-}
-
-struct AnyAndHostInfo {
-    any: Box<dyn Any>,
-    host_info: Option<Box<dyn Any>>,
-}
-
-#[derive(Clone)]
-pub struct OtherRef(Rc<RefCell<AnyAndHostInfo>>);
+use wasmtime_runtime::VMExternRef;
 
 /// Represents an opaque reference to any data within WebAssembly.
 #[derive(Clone)]
-pub enum ExternRef {
-    /// A reference to no data.
-    Null,
-    /// A reference to data stored internally in `wasmtime`.
-    Ref(InternalRef),
-    /// A reference to data located outside of `wasmtime`.
-    Other(OtherRef),
+pub struct ExternRef {
+    pub(crate) inner: VMExternRef,
+    pub(crate) store: Weak<crate::runtime::StoreInner>,
 }
 
 impl ExternRef {
-    /// Creates a new instance of `ExternRef` from `Box<dyn Any>`.
-    pub fn new(data: Box<dyn Any>) -> Self {
-        let info = AnyAndHostInfo {
-            any: data,
-            host_info: None,
-        };
-        ExternRef::Other(OtherRef(Rc::new(RefCell::new(info))))
+    /// Creates a new instance of `ExternRef` wrapping the given value.
+    pub fn new<T>(store: &crate::Store, value: T) -> ExternRef
+    where
+        T: 'static + Any,
+    {
+        let inner = VMExternRef::new(value);
+        let store = store.weak();
+        ExternRef { inner, store }
     }
 
     /// Creates a `Null` reference.
-    pub fn null() -> Self {
-        ExternRef::Null
+    pub fn null() -> Option<Self> {
+        None
     }
 
-    /// Returns the data stored in the reference if available.
-    /// # Panics
-    /// Panics if the variant isn't `ExternRef::Other`.
-    pub fn data(&self) -> cell::Ref<Box<dyn Any>> {
-        match self {
-            ExternRef::Other(OtherRef(r)) => cell::Ref::map(r.borrow(), |r| &r.any),
-            _ => panic!("expected ExternRef::Other"),
-        }
+    /// Get this reference's store.
+    ///
+    /// Returns `None` if this reference outlived its store.
+    pub fn store(&self) -> Option<crate::runtime::Store> {
+        crate::runtime::Store::upgrade(&self.store)
     }
 
-    /// Returns true if the two `ExternRef<T>`'s point to the same value (not just
-    /// values that compare as equal).
+    /// Get the underlying data for this `ExternRef`.
+    pub fn data(&self) -> &dyn Any {
+        &*self.inner
+    }
+
+    /// Does this `ExternRef` point to the same inner value as `other`?0
+    ///
+    /// This is *only* pointer equality, and does *not* run any inner value's
+    /// `Eq` implementation.
     pub fn ptr_eq(&self, other: &ExternRef) -> bool {
-        match (self, other) {
-            (ExternRef::Null, ExternRef::Null) => true,
-            (ExternRef::Ref(InternalRef(ref a)), ExternRef::Ref(InternalRef(ref b))) => {
-                a.ptr_eq(b.as_ref())
-            }
-            (ExternRef::Other(OtherRef(ref a)), ExternRef::Other(OtherRef(ref b))) => {
-                Rc::ptr_eq(a, b)
-            }
-            _ => false,
-        }
+        self.inner == other.inner
     }
 
-    /// Returns a mutable reference to the host information if available.
-    /// # Panics
-    /// Panics if `ExternRef` is already borrowed or `ExternRef` is `Null`.
-    pub fn host_info(&self) -> Option<cell::RefMut<Box<dyn Any>>> {
-        match self {
-            ExternRef::Null => panic!("null"),
-            ExternRef::Ref(r) => r.0.host_info(),
-            ExternRef::Other(r) => {
-                let info = cell::RefMut::map(r.0.borrow_mut(), |b| &mut b.host_info);
-                if info.is_none() {
-                    return None;
-                }
-                Some(cell::RefMut::map(info, |info| info.as_mut().unwrap()))
-            }
-        }
+    /// Returns the host information for this `externref`, if previously created
+    /// with `set_host_info`.
+    pub fn host_info(&self) -> Option<Rc<RefCell<dyn Any>>> {
+        let store = crate::Store::upgrade(&self.store)?;
+        store.host_info(self)
     }
 
-    /// Sets the host information for an `ExternRef`.
-    /// # Panics
-    /// Panics if `ExternRef` is already borrowed or `ExternRef` is `Null`.
-    pub fn set_host_info(&self, info: Option<Box<dyn Any>>) {
-        match self {
-            ExternRef::Null => panic!("null"),
-            ExternRef::Ref(r) => r.0.set_host_info(info),
-            ExternRef::Other(r) => {
-                r.0.borrow_mut().host_info = info;
-            }
-        }
+    /// Set the host information for this `externref`, returning the old host
+    /// information if it was previously set.
+    pub fn set_host_info<T>(&self, info: T) -> Option<Rc<RefCell<dyn Any>>>
+    where
+        T: 'static + Any,
+    {
+        let store = crate::Store::upgrade(&self.store)?;
+        store.set_host_info(self, Some(Rc::new(RefCell::new(info))))
+    }
+
+    /// Remove the host information for this `externref`, returning the old host
+    /// information if it was previously set.
+    pub fn remove_host_info(&self) -> Option<Rc<RefCell<dyn Any>>> {
+        let store = crate::Store::upgrade(&self.store)?;
+        store.set_host_info(self, None)
     }
 }
 
 impl fmt::Debug for ExternRef {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            ExternRef::Null => write!(f, "null"),
-            ExternRef::Ref(_) => write!(f, "externref"),
-            ExternRef::Other(_) => write!(f, "other ref"),
-        }
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let ExternRef { inner, store: _ } = self;
+        f.debug_struct("ExternRef")
+            .field("inner", &inner)
+            .field("store", &"..")
+            .finish()
     }
 }
 
-struct ContentBox<T> {
-    content: T,
-    host_info: Option<Box<dyn Any>>,
-    externref_data: Weak<dyn InternalRefBase>,
-}
-
 /// Represents a piece of data located in the host environment.
-pub struct HostRef<T>(Rc<RefCell<ContentBox<T>>>);
+#[derive(Debug)]
+pub struct HostRef<T>
+where
+    T: 'static + Any,
+{
+    externref: ExternRef,
+    _phantom: PhantomData<T>,
+}
 
-impl<T: 'static> HostRef<T> {
+impl<T> HostRef<T>
+where
+    T: 'static + Any,
+{
     /// Creates a new `HostRef<T>` from `T`.
-    pub fn new(item: T) -> HostRef<T> {
-        let externref_data: Weak<HostRef<T>> = Weak::new();
-        let content = ContentBox {
-            content: item,
-            host_info: None,
-            externref_data,
-        };
-        HostRef(Rc::new(RefCell::new(content)))
+    pub fn new(store: &crate::Store, item: T) -> HostRef<T> {
+        HostRef {
+            externref: ExternRef::new(store, RefCell::new(item)),
+            _phantom: PhantomData,
+        }
     }
 
     /// Immutably borrows the wrapped data.
+    ///
     /// # Panics
+    ///
     /// Panics if the value is currently mutably borrowed.
     pub fn borrow(&self) -> cell::Ref<T> {
-        cell::Ref::map(self.0.borrow(), |b| &b.content)
+        self.inner().borrow()
     }
 
     /// Mutably borrows the wrapped data.
+    ///
     /// # Panics
+    ///
     /// Panics if the `HostRef<T>` is already borrowed.
     pub fn borrow_mut(&self) -> cell::RefMut<T> {
-        cell::RefMut::map(self.0.borrow_mut(), |b| &mut b.content)
+        self.inner().borrow_mut()
     }
 
     /// Returns true if the two `HostRef<T>`'s point to the same value (not just
     /// values that compare as equal).
     pub fn ptr_eq(&self, other: &HostRef<T>) -> bool {
-        Rc::ptr_eq(&self.0, &other.0)
+        self.externref.ptr_eq(&other.externref)
     }
 
-    /// Returns an opaque reference to the wrapped data in the form of
-    /// an `ExternRef`.
-    /// # Panics
-    /// Panics if `HostRef<T>` is already mutably borrowed.
-    pub fn externref(&self) -> ExternRef {
-        let r = self.0.borrow_mut().externref_data.upgrade();
-        if let Some(r) = r {
-            return ExternRef::Ref(InternalRef(r));
-        }
-        let externref_data: Rc<dyn InternalRefBase> = Rc::new(self.clone());
-        self.0.borrow_mut().externref_data = Rc::downgrade(&externref_data);
-        ExternRef::Ref(InternalRef(externref_data))
+    fn inner(&self) -> &RefCell<T> {
+        self.externref
+            .inner
+            .downcast_ref::<RefCell<T>>()
+            .expect("`HostRef<T>`s always wrap an `ExternRef` of `RefCell<T>`")
     }
 }
 
-impl<T: 'static> InternalRefBase for HostRef<T> {
-    fn ptr_eq(&self, other: &dyn InternalRefBase) -> bool {
-        if let Some(other) = other.as_any().downcast_ref() {
-            self.ptr_eq(other)
+impl<T> AsRef<ExternRef> for HostRef<T> {
+    fn as_ref(&self) -> &ExternRef {
+        &self.externref
+    }
+}
+
+impl<T> From<HostRef<T>> for ExternRef
+where
+    T: 'static + Any,
+{
+    fn from(host: HostRef<T>) -> ExternRef {
+        host.externref
+    }
+}
+
+impl<T> TryFrom<ExternRef> for HostRef<T>
+where
+    T: 'static + Any,
+{
+    type Error = ExternRef;
+
+    fn try_from(externref: ExternRef) -> Result<Self, ExternRef> {
+        if externref.inner.is::<RefCell<T>>() {
+            Ok(HostRef {
+                externref,
+                _phantom: PhantomData,
+            })
         } else {
-            false
+            Err(externref)
         }
     }
-
-    fn as_any(&self) -> &dyn Any {
-        self
-    }
-
-    fn host_info(&self) -> Option<cell::RefMut<Box<dyn Any>>> {
-        let info = cell::RefMut::map(self.0.borrow_mut(), |b| &mut b.host_info);
-        if info.is_none() {
-            return None;
-        }
-        Some(cell::RefMut::map(info, |info| info.as_mut().unwrap()))
-    }
-
-    fn set_host_info(&self, info: Option<Box<dyn Any>>) {
-        self.0.borrow_mut().host_info = info;
-    }
 }
 
 impl<T> Clone for HostRef<T> {
     fn clone(&self) -> HostRef<T> {
-        HostRef(self.0.clone())
-    }
-}
-
-impl<T: fmt::Debug> fmt::Debug for HostRef<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "Ref(")?;
-        self.0.borrow().content.fmt(f)?;
-        write!(f, ")")
+        HostRef {
+            externref: self.externref.clone(),
+            _phantom: PhantomData,
+        }
     }
 }
diff --git a/crates/wasmtime/src/runtime.rs b/crates/wasmtime/src/runtime.rs
index 23168d8800..4c1c514bc8 100644
--- a/crates/wasmtime/src/runtime.rs
+++ b/crates/wasmtime/src/runtime.rs
@@ -1,8 +1,11 @@
 use crate::externals::MemoryCreator;
+use crate::r#ref::ExternRef;
 use crate::trampoline::{MemoryCreatorProxy, StoreInstanceHandle};
 use anyhow::{bail, Result};
+use std::any::Any;
 use std::cell::RefCell;
 use std::cmp;
+use std::collections::HashMap;
 use std::convert::TryFrom;
 use std::fmt;
 use std::path::Path;
@@ -14,7 +17,7 @@ use wasmtime_environ::{CacheConfig, Tunables};
 use wasmtime_jit::{native, CompilationStrategy, Compiler};
 use wasmtime_profiling::{JitDumpAgent, NullProfilerAgent, ProfilingAgent, VTuneAgent};
 use wasmtime_runtime::{
-    debug_builtins, InstanceHandle, RuntimeMemoryCreator, SignalHandler, VMInterrupts,
+    debug_builtins, InstanceHandle, RuntimeMemoryCreator, SignalHandler, VMExternRef, VMInterrupts,
 };
 
 // Runtime Environment
@@ -733,6 +736,7 @@ pub(crate) struct StoreInner {
     compiler: RefCell<Compiler>,
     instances: RefCell<Vec<InstanceHandle>>,
     signal_handler: RefCell<Option<Box<SignalHandler<'static>>>>,
+    host_info: RefCell<HashMap<VMExternRef, Rc<RefCell<dyn Any>>>>,
 }
 
 impl Store {
@@ -758,6 +762,7 @@ impl Store {
                 compiler: RefCell::new(compiler),
                 instances: RefCell::new(Vec::new()),
                 signal_handler: RefCell::new(None),
+                host_info: RefCell::new(HashMap::new()),
             }),
         }
     }
@@ -809,6 +814,37 @@ impl Store {
         Rc::downgrade(&self.inner)
     }
 
+    pub(crate) fn upgrade(weak: &Weak<StoreInner>) -> Option<Self> {
+        let inner = weak.upgrade()?;
+        Some(Self { inner })
+    }
+
+    pub(crate) fn host_info(&self, externref: &ExternRef) -> Option<Rc<RefCell<dyn Any>>> {
+        debug_assert!(
+            std::rc::Weak::ptr_eq(&self.weak(), &externref.store),
+            "externref must be from this store"
+        );
+        let infos = self.inner.host_info.borrow();
+        infos.get(&externref.inner).cloned()
+    }
+
+    pub(crate) fn set_host_info(
+        &self,
+        externref: &ExternRef,
+        info: Option<Rc<RefCell<dyn Any>>>,
+    ) -> Option<Rc<RefCell<dyn Any>>> {
+        debug_assert!(
+            std::rc::Weak::ptr_eq(&self.weak(), &externref.store),
+            "externref must be from this store"
+        );
+        let mut infos = self.inner.host_info.borrow_mut();
+        if let Some(info) = info {
+            infos.insert(externref.inner.clone(), info)
+        } else {
+            infos.remove(&externref.inner)
+        }
+    }
+
     pub(crate) fn signal_handler(&self) -> std::cell::Ref<'_, Option<Box<SignalHandler<'static>>>> {
         self.inner.signal_handler.borrow()
     }
diff --git a/crates/wasmtime/src/trampoline/create_handle.rs b/crates/wasmtime/src/trampoline/create_handle.rs
index 428c6c35ac..6d78d49f07 100644
--- a/crates/wasmtime/src/trampoline/create_handle.rs
+++ b/crates/wasmtime/src/trampoline/create_handle.rs
@@ -32,7 +32,12 @@ pub(crate) fn create_handle(
         .local
         .signatures
         .values()
-        .map(|sig| store.compiler().signatures().register(sig))
+        .map(|(wasm, native)| {
+            store
+                .compiler()
+                .signatures()
+                .register(wasm.clone(), native.clone())
+        })
         .collect::<PrimaryMap<_, _>>();
 
     unsafe {
diff --git a/crates/wasmtime/src/trampoline/func.rs b/crates/wasmtime/src/trampoline/func.rs
index 41d6ac61b3..1c3a4a31d9 100644
--- a/crates/wasmtime/src/trampoline/func.rs
+++ b/crates/wasmtime/src/trampoline/func.rs
@@ -225,7 +225,10 @@ pub fn create_handle_with_function(
 
     // First up we manufacture a trampoline which has the ABI specified by `ft`
     // and calls into `stub_fn`...
-    let sig_id = module.local.signatures.push(sig.clone());
+    let sig_id = module
+        .local
+        .signatures
+        .push((ft.to_wasm_func_type(), sig.clone()));
     let func_id = module.local.functions.push(sig_id);
     module
         .exports
@@ -244,7 +247,10 @@ pub fn create_handle_with_function(
         mem::size_of::<u128>(),
     )?;
     assert!(relocations.is_empty());
-    let sig_id = store.compiler().signatures().register(&sig);
+    let sig_id = store
+        .compiler()
+        .signatures()
+        .register(ft.to_wasm_func_type(), sig);
     trampolines.insert(sig_id, trampoline);
 
     // Next up we wrap everything up into an `InstanceHandle` by publishing our
@@ -285,13 +291,19 @@ pub unsafe fn create_handle_with_raw_function(
     let mut finished_functions = PrimaryMap::new();
     let mut trampolines = HashMap::new();
 
-    let sig_id = module.local.signatures.push(sig.clone());
+    let sig_id = module
+        .local
+        .signatures
+        .push((ft.to_wasm_func_type(), sig.clone()));
     let func_id = module.local.functions.push(sig_id);
     module
         .exports
         .insert("trampoline".to_string(), EntityIndex::Function(func_id));
     finished_functions.push(func);
-    let sig_id = store.compiler().signatures().register(&sig);
+    let sig_id = store
+        .compiler()
+        .signatures()
+        .register(ft.to_wasm_func_type(), sig);
     trampolines.insert(sig_id, trampoline);
 
     create_handle(module, store, finished_functions, trampolines, state)
diff --git a/crates/wasmtime/src/types.rs b/crates/wasmtime/src/types.rs
index e03c6e41c0..75c67ae188 100644
--- a/crates/wasmtime/src/types.rs
+++ b/crates/wasmtime/src/types.rs
@@ -67,6 +67,20 @@ pub enum ValType {
     FuncRef,
 }
 
+impl fmt::Display for ValType {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            ValType::I32 => write!(f, "i32"),
+            ValType::I64 => write!(f, "i64"),
+            ValType::F32 => write!(f, "f32"),
+            ValType::F64 => write!(f, "f64"),
+            ValType::V128 => write!(f, "v128"),
+            ValType::ExternRef => write!(f, "externref"),
+            ValType::FuncRef => write!(f, "funcref"),
+        }
+    }
+}
+
 impl ValType {
     /// Returns true if `ValType` matches any of the numeric types. (e.g. `I32`,
     /// `I64`, `F32`, `F64`).
@@ -106,6 +120,31 @@ impl ValType {
             _ => None,
         }
     }
+
+    pub(crate) fn to_wasm_type(&self) -> wasm::WasmType {
+        match self {
+            Self::I32 => wasm::WasmType::I32,
+            Self::I64 => wasm::WasmType::I64,
+            Self::F32 => wasm::WasmType::F32,
+            Self::F64 => wasm::WasmType::F64,
+            Self::V128 => wasm::WasmType::V128,
+            Self::FuncRef => wasm::WasmType::FuncRef,
+            Self::ExternRef => wasm::WasmType::ExternRef,
+        }
+    }
+
+    pub(crate) fn from_wasm_type(ty: &wasm::WasmType) -> Option<Self> {
+        match ty {
+            wasm::WasmType::I32 => Some(Self::I32),
+            wasm::WasmType::I64 => Some(Self::I64),
+            wasm::WasmType::F32 => Some(Self::F32),
+            wasm::WasmType::F64 => Some(Self::F64),
+            wasm::WasmType::V128 => Some(Self::V128),
+            wasm::WasmType::FuncRef => Some(Self::FuncRef),
+            wasm::WasmType::ExternRef => Some(Self::ExternRef),
+            wasm::WasmType::Func | wasm::WasmType::EmptyBlockType => None,
+        }
+    }
 }
 
 // External Types
@@ -184,12 +223,6 @@ impl From<TableType> for ExternType {
     }
 }
 
-// Function Types
-fn from_wasmtime_abiparam(param: &ir::AbiParam) -> Option<ValType> {
-    assert_eq!(param.purpose, ir::ArgumentPurpose::Normal);
-    ValType::from_wasmtime_type(param.value_type)
-}
-
 /// A descriptor for a function in a WebAssembly module.
 ///
 /// WebAssembly functions can have 0 or more parameters and results.
@@ -218,6 +251,13 @@ impl FuncType {
         &self.results
     }
 
+    pub(crate) fn to_wasm_func_type(&self) -> wasm::WasmFuncType {
+        wasm::WasmFuncType {
+            params: self.params.iter().map(|p| p.to_wasm_type()).collect(),
+            returns: self.results.iter().map(|r| r.to_wasm_type()).collect(),
+        }
+    }
+
     /// Returns `Some` if this function signature was compatible with cranelift,
     /// or `None` if one of the types/results wasn't supported or compatible
     /// with cranelift.
@@ -251,17 +291,16 @@ impl FuncType {
     /// Returns `None` if any types in the signature can't be converted to the
     /// types in this crate, but that should very rarely happen and largely only
     /// indicate a bug in our cranelift integration.
-    pub(crate) fn from_wasmtime_signature(signature: &ir::Signature) -> Option<FuncType> {
+    pub(crate) fn from_wasm_func_type(signature: &wasm::WasmFuncType) -> Option<FuncType> {
         let params = signature
             .params
             .iter()
-            .skip(2) // skip the caller/callee vmctx
-            .map(|p| from_wasmtime_abiparam(p))
+            .map(|p| ValType::from_wasm_type(p))
             .collect::<Option<Vec<_>>>()?;
         let results = signature
             .returns
             .iter()
-            .map(|p| from_wasmtime_abiparam(p))
+            .map(|r| ValType::from_wasm_type(r))
             .collect::<Option<Vec<_>>>()?;
         Some(FuncType {
             params: params.into_boxed_slice(),
@@ -390,7 +429,7 @@ impl MemoryType {
 
 #[derive(Clone, Hash, Eq, PartialEq)]
 pub(crate) enum EntityType<'module> {
-    Function(&'module ir::Signature),
+    Function(&'module wasm::WasmFuncType),
     Table(&'module wasm::Table),
     Memory(&'module wasm::Memory),
     Global(&'module wasm::Global),
@@ -404,7 +443,7 @@ impl<'module> EntityType<'module> {
     ) -> EntityType<'module> {
         match entity_index {
             EntityIndex::Function(func_index) => {
-                let sig = module.local.func_signature(*func_index);
+                let sig = module.local.wasm_func_type(*func_index);
                 EntityType::Function(&sig)
             }
             EntityIndex::Table(table_index) => {
@@ -422,7 +461,7 @@ impl<'module> EntityType<'module> {
     /// Convert this `EntityType` to an `ExternType`.
     pub(crate) fn extern_type(&self) -> ExternType {
         match self {
-            EntityType::Function(sig) => FuncType::from_wasmtime_signature(sig)
+            EntityType::Function(sig) => FuncType::from_wasm_func_type(sig)
                 .expect("core wasm function type should be supported")
                 .into(),
             EntityType::Table(table) => TableType::from_wasmtime_table(table).into(),
diff --git a/crates/wasmtime/src/values.rs b/crates/wasmtime/src/values.rs
index c0b8dd8102..07588cabb8 100644
--- a/crates/wasmtime/src/values.rs
+++ b/crates/wasmtime/src/values.rs
@@ -2,6 +2,7 @@ use crate::r#ref::ExternRef;
 use crate::{Func, Store, ValType};
 use anyhow::{bail, Result};
 use std::ptr;
+use wasmtime_runtime::VMExternRef;
 
 /// Possible runtime values that a WebAssembly module can either consume or
 /// produce.
@@ -26,9 +27,7 @@ pub enum Val {
     F64(u64),
 
     /// An `externref` value which can hold opaque data to the wasm instance itself.
-    ///
-    /// Note that this is a nullable value as well.
-    ExternRef(ExternRef),
+    ExternRef(Option<ExternRef>),
 
     /// A first-class reference to a WebAssembly function.
     FuncRef(Func),
@@ -87,18 +86,31 @@ impl Val {
             Val::F32(u) => ptr::write(p as *mut u32, *u),
             Val::F64(u) => ptr::write(p as *mut u64, *u),
             Val::V128(b) => ptr::write(p as *mut u128, *b),
+            Val::ExternRef(None) => ptr::write(p, 0),
+            Val::ExternRef(Some(x)) => ptr::write(p as *mut *mut u8, x.inner.clone().into_raw()),
             _ => unimplemented!("Val::write_value_to"),
         }
     }
 
-    pub(crate) unsafe fn read_value_from(p: *const u128, ty: &ValType) -> Val {
+    pub(crate) unsafe fn read_value_from(store: &Store, p: *const u128, ty: &ValType) -> Val {
         match ty {
             ValType::I32 => Val::I32(ptr::read(p as *const i32)),
             ValType::I64 => Val::I64(ptr::read(p as *const i64)),
             ValType::F32 => Val::F32(ptr::read(p as *const u32)),
             ValType::F64 => Val::F64(ptr::read(p as *const u64)),
             ValType::V128 => Val::V128(ptr::read(p as *const u128)),
-            _ => unimplemented!("Val::read_value_from"),
+            ValType::ExternRef => {
+                let raw = ptr::read(p as *const *mut u8);
+                if raw.is_null() {
+                    Val::ExternRef(None)
+                } else {
+                    Val::ExternRef(Some(ExternRef {
+                        inner: VMExternRef::from_raw(raw),
+                        store: store.weak(),
+                    }))
+                }
+            }
+            _ => unimplemented!("Val::read_value_from: {:?}", ty),
         }
     }
 
@@ -112,24 +124,31 @@ impl Val {
         (V128(u128) v128 unwrap_v128 *e)
     }
 
-    /// Attempt to access the underlying value of this `Val`, returning
-    /// `None` if it is not the correct type.
+    /// Attempt to access the underlying `externref` value of this `Val`.
     ///
-    /// This will return `Some` for both the `ExternRef` and `FuncRef` types.
-    pub fn externref(&self) -> Option<ExternRef> {
+    /// If this is not an `externref`, then `None` is returned.
+    ///
+    /// If this is a null `externref`, then `Some(None)` is returned.
+    ///
+    /// If this is a non-null `externref`, then `Some(Some(..))` is returned.
+    pub fn externref(&self) -> Option<Option<ExternRef>> {
         match self {
             Val::ExternRef(e) => Some(e.clone()),
             _ => None,
         }
     }
 
-    /// Returns the underlying value of this `Val`, panicking if it's the
+    /// Returns the underlying `externref` value of this `Val`, panicking if it's the
     /// wrong type.
     ///
+    /// If this is a null `externref`, then `None` is returned.
+    ///
+    /// If this is a non-null `externref`, then `Some(..)` is returned.
+    ///
     /// # Panics
     ///
-    /// Panics if `self` is not of the right type.
-    pub fn unwrap_externref(&self) -> ExternRef {
+    /// Panics if `self` is not a (nullable) `externref`.
+    pub fn unwrap_externref(&self) -> Option<ExternRef> {
         self.externref().expect("expected externref")
     }
 
@@ -140,8 +159,8 @@ impl Val {
             // TODO: need to implement this once we actually finalize what
             // `externref` will look like and it's actually implemented to pass it
             // to compiled wasm as well.
-            Val::ExternRef(ExternRef::Ref(_)) | Val::ExternRef(ExternRef::Other(_)) => false,
-            Val::ExternRef(ExternRef::Null) => true,
+            Val::ExternRef(Some(e)) => e.store.ptr_eq(&store.weak()),
+            Val::ExternRef(None) => true,
 
             // Integers have no association with any particular store, so
             // they're always considered as "yes I came from that store",
@@ -176,6 +195,12 @@ impl From<f64> for Val {
 
 impl From<ExternRef> for Val {
     fn from(val: ExternRef) -> Val {
+        Val::ExternRef(Some(val))
+    }
+}
+
+impl From<Option<ExternRef>> for Val {
+    fn from(val: Option<ExternRef>) -> Val {
         Val::ExternRef(val)
     }
 }
@@ -194,7 +219,7 @@ pub(crate) fn into_checked_anyfunc(
         bail!("cross-`Store` values are not supported");
     }
     Ok(match val {
-        Val::ExternRef(ExternRef::Null) => wasmtime_runtime::VMCallerCheckedAnyfunc {
+        Val::ExternRef(None) => wasmtime_runtime::VMCallerCheckedAnyfunc {
             func_ptr: ptr::null(),
             type_index: wasmtime_runtime::VMSharedSignatureIndex::default(),
             vmctx: ptr::null_mut(),
@@ -216,7 +241,7 @@ pub(crate) fn from_checked_anyfunc(
     store: &Store,
 ) -> Val {
     if item.type_index == wasmtime_runtime::VMSharedSignatureIndex::default() {
-        return Val::ExternRef(ExternRef::Null);
+        return Val::ExternRef(None);
     }
     let instance_handle = unsafe { wasmtime_runtime::InstanceHandle::from_vmctx(item.vmctx) };
     let export = wasmtime_runtime::ExportFunction {
diff --git a/crates/wast/src/spectest.rs b/crates/wast/src/spectest.rs
index ed10b77862..f49125dbe8 100644
--- a/crates/wast/src/spectest.rs
+++ b/crates/wast/src/spectest.rs
@@ -35,7 +35,7 @@ pub fn link_spectest(linker: &mut Linker) -> Result<()> {
     linker.define("spectest", "global_f64", g)?;
 
     let ty = TableType::new(ValType::FuncRef, Limits::new(10, Some(20)));
-    let table = Table::new(linker.store(), ty, Val::ExternRef(ExternRef::Null))?;
+    let table = Table::new(linker.store(), ty, Val::ExternRef(None))?;
     linker.define("spectest", "table", table)?;
 
     let ty = MemoryType::new(Limits::new(1, Some(2)));
diff --git a/crates/wast/src/wast.rs b/crates/wast/src/wast.rs
index 5574525dae..303df76100 100644
--- a/crates/wast/src/wast.rs
+++ b/crates/wast/src/wast.rs
@@ -3,11 +3,14 @@ use anyhow::{anyhow, bail, Context as _, Result};
 use std::path::Path;
 use std::str;
 use wasmtime::*;
-use wast::parser::{self, ParseBuffer};
 use wast::Wat;
+use wast::{
+    parser::{self, ParseBuffer},
+    RefType,
+};
 
 /// Translate from a `script::Value` to a `RuntimeValue`.
-fn runtime_value(v: &wast::Expression<'_>) -> Result<Val> {
+fn runtime_value(store: &Store, v: &wast::Expression<'_>) -> Result<Val> {
     use wast::Instruction::*;
 
     if v.instrs.len() != 1 {
@@ -19,6 +22,8 @@ fn runtime_value(v: &wast::Expression<'_>) -> Result<Val> {
         F32Const(x) => Val::F32(x.bits),
         F64Const(x) => Val::F64(x.bits),
         V128Const(x) => Val::V128(u128::from_le_bytes(x.to_le_bytes())),
+        RefNull(RefType::Extern) => Val::ExternRef(None),
+        RefExtern(x) => Val::ExternRef(Some(ExternRef::new(store, *x))),
         other => bail!("couldn't convert {:?} to a runtime value", other),
     })
 }
@@ -114,7 +119,7 @@ impl WastContext {
         let values = exec
             .args
             .iter()
-            .map(runtime_value)
+            .map(|v| runtime_value(&self.store, v))
             .collect::<Result<Vec<_>>>()?;
         self.invoke(exec.module.map(|i| i.name()), exec.name, &values)
     }
@@ -403,6 +408,18 @@ fn val_matches(actual: &Val, expected: &wast::AssertExpression) -> Result<bool>
         (Val::F32(a), wast::AssertExpression::F32(b)) => f32_matches(*a, b),
         (Val::F64(a), wast::AssertExpression::F64(b)) => f64_matches(*a, b),
         (Val::V128(a), wast::AssertExpression::V128(b)) => v128_matches(*a, b),
+        (Val::ExternRef(x), wast::AssertExpression::RefNull(wast::RefType::Extern)) => x.is_none(),
+        (Val::ExternRef(x), wast::AssertExpression::RefExtern(y)) => {
+            if let Some(x) = x {
+                let x = x
+                    .data()
+                    .downcast_ref::<u32>()
+                    .expect("only u32 externrefs created in wast test suites");
+                x == y
+            } else {
+                false
+            }
+        }
         _ => bail!(
             "don't know how to compare {:?} and {:?} yet",
             actual,
diff --git a/tests/all/externals.rs b/tests/all/externals.rs
index 0919f13685..281365d18e 100644
--- a/tests/all/externals.rs
+++ b/tests/all/externals.rs
@@ -28,47 +28,27 @@ fn bad_tables() {
 
     // get out of bounds
     let ty = TableType::new(ValType::FuncRef, Limits::new(0, Some(1)));
-    let t = Table::new(
-        &Store::default(),
-        ty.clone(),
-        Val::ExternRef(ExternRef::Null),
-    )
-    .unwrap();
+    let t = Table::new(&Store::default(), ty.clone(), Val::ExternRef(None)).unwrap();
     assert!(t.get(0).is_none());
     assert!(t.get(u32::max_value()).is_none());
 
     // set out of bounds or wrong type
     let ty = TableType::new(ValType::FuncRef, Limits::new(1, Some(1)));
-    let t = Table::new(
-        &Store::default(),
-        ty.clone(),
-        Val::ExternRef(ExternRef::Null),
-    )
-    .unwrap();
+    let t = Table::new(&Store::default(), ty.clone(), Val::ExternRef(None)).unwrap();
     assert!(t.set(0, Val::I32(0)).is_err());
-    assert!(t.set(0, Val::ExternRef(ExternRef::Null)).is_ok());
-    assert!(t.set(1, Val::ExternRef(ExternRef::Null)).is_err());
+    assert!(t.set(0, Val::ExternRef(None)).is_ok());
+    assert!(t.set(1, Val::ExternRef(None)).is_err());
 
     // grow beyond max
     let ty = TableType::new(ValType::FuncRef, Limits::new(1, Some(1)));
-    let t = Table::new(
-        &Store::default(),
-        ty.clone(),
-        Val::ExternRef(ExternRef::Null),
-    )
-    .unwrap();
-    assert!(t.grow(0, Val::ExternRef(ExternRef::Null)).is_ok());
-    assert!(t.grow(1, Val::ExternRef(ExternRef::Null)).is_err());
+    let t = Table::new(&Store::default(), ty.clone(), Val::ExternRef(None)).unwrap();
+    assert!(t.grow(0, Val::ExternRef(None)).is_ok());
+    assert!(t.grow(1, Val::ExternRef(None)).is_err());
     assert_eq!(t.size(), 1);
 
     // grow wrong type
     let ty = TableType::new(ValType::FuncRef, Limits::new(1, Some(2)));
-    let t = Table::new(
-        &Store::default(),
-        ty.clone(),
-        Val::ExternRef(ExternRef::Null),
-    )
-    .unwrap();
+    let t = Table::new(&Store::default(), ty.clone(), Val::ExternRef(None)).unwrap();
     assert!(t.grow(1, Val::I32(0)).is_err());
     assert_eq!(t.size(), 1);
 }
@@ -88,7 +68,7 @@ fn cross_store() -> anyhow::Result<()> {
     let ty = MemoryType::new(Limits::new(1, None));
     let memory = Memory::new(&store2, ty);
     let ty = TableType::new(ValType::FuncRef, Limits::new(1, None));
-    let table = Table::new(&store2, ty, Val::ExternRef(ExternRef::Null))?;
+    let table = Table::new(&store2, ty, Val::ExternRef(None))?;
 
     let need_func = Module::new(&store1, r#"(module (import "" "" (func)))"#)?;
     assert!(Instance::new(&need_func, &[func.into()]).is_err());
diff --git a/tests/all/linker.rs b/tests/all/linker.rs
index b2c7a64da5..958dcc8ecc 100644
--- a/tests/all/linker.rs
+++ b/tests/all/linker.rs
@@ -56,11 +56,11 @@ fn link_twice_bad() -> Result<()> {
 
     // tables
     let ty = TableType::new(ValType::FuncRef, Limits::new(1, None));
-    let table = Table::new(&store, ty, Val::ExternRef(ExternRef::Null))?;
+    let table = Table::new(&store, ty, Val::ExternRef(None))?;
     linker.define("", "", table.clone())?;
     assert!(linker.define("", "", table.clone()).is_err());
     let ty = TableType::new(ValType::FuncRef, Limits::new(2, None));
-    let table = Table::new(&store, ty, Val::ExternRef(ExternRef::Null))?;
+    let table = Table::new(&store, ty, Val::ExternRef(None))?;
     assert!(linker.define("", "", table.clone()).is_err());
     Ok(())
 }
diff --git a/tests/all/table.rs b/tests/all/table.rs
index f7599e87cc..9bf7cb4cc4 100644
--- a/tests/all/table.rs
+++ b/tests/all/table.rs
@@ -4,9 +4,9 @@ use wasmtime::*;
 fn get_none() {
     let store = Store::default();
     let ty = TableType::new(ValType::FuncRef, Limits::new(1, None));
-    let table = Table::new(&store, ty, Val::ExternRef(ExternRef::Null)).unwrap();
+    let table = Table::new(&store, ty, Val::ExternRef(None)).unwrap();
     match table.get(0) {
-        Some(Val::ExternRef(ExternRef::Null)) => {}
+        Some(Val::ExternRef(None)) => {}
         _ => panic!(),
     }
     assert!(table.get(1).is_none());
diff --git a/tests/all/traps.rs b/tests/all/traps.rs
index 575e6741b8..f6cc691a6b 100644
--- a/tests/all/traps.rs
+++ b/tests/all/traps.rs
@@ -341,7 +341,7 @@ fn mismatched_arguments() -> Result<()> {
     );
     assert_eq!(
         func.call(&[Val::F32(0)]).unwrap_err().to_string(),
-        "argument type mismatch",
+        "argument type mismatch: found f32 but expected i32",
     );
     assert_eq!(
         func.call(&[Val::I32(0), Val::I32(1)])
diff --git a/tests/all/use_after_drop.rs b/tests/all/use_after_drop.rs
index 67edfc158a..625bac897f 100644
--- a/tests/all/use_after_drop.rs
+++ b/tests/all/use_after_drop.rs
@@ -11,7 +11,7 @@ fn use_func_after_drop() -> Result<()> {
             assert_eq!(closed_over_data, "abcd");
         });
         let ty = TableType::new(ValType::FuncRef, Limits::new(1, None));
-        table = Table::new(&store, ty, Val::ExternRef(ExternRef::Null))?;
+        table = Table::new(&store, ty, Val::ExternRef(None))?;
         table.set(0, func.into())?;
     }
     let func = table.get(0).unwrap().funcref().unwrap().clone();
diff --git a/tests/misc_testsuite/reference-types/externref-id-function.wast b/tests/misc_testsuite/reference-types/externref-id-function.wast
new file mode 100644
index 0000000000..0262d33f9c
--- /dev/null
+++ b/tests/misc_testsuite/reference-types/externref-id-function.wast
@@ -0,0 +1,8 @@
+(module
+  (func (export "identity") (param externref) (result externref)
+    local.get 0))
+
+(assert_return (invoke "identity" (ref.null extern))
+               (ref.null extern))
+(assert_return (invoke "identity" (ref.extern 1))
+               (ref.extern 1))