diff --git a/lib/environ/Cargo.toml b/lib/environ/Cargo.toml
index be3cd4375c..5cd2d730f0 100644
--- a/lib/environ/Cargo.toml
+++ b/lib/environ/Cargo.toml
@@ -17,11 +17,12 @@ cranelift-wasm = "0.26.0"
 cast = { version = "0.2.2", default-features = false }
 failure = { version = "0.1.3", default-features = false }
 failure_derive = { version = "0.1.3", default-features = false }
+hashmap_core = { version = "0.1.9", optional = true }
 
 [features]
 default = ["std"]
 std = ["cranelift-codegen/std", "cranelift-wasm/std"]
-core = ["cranelift-codegen/core", "cranelift-wasm/core"]
+core = ["hashmap_core", "cranelift-codegen/core", "cranelift-wasm/core"]
 
 [badges]
 maintenance = { status = "experimental" }
diff --git a/lib/environ/src/func_environ.rs b/lib/environ/src/func_environ.rs
index 2ec672f021..588546defb 100644
--- a/lib/environ/src/func_environ.rs
+++ b/lib/environ/src/func_environ.rs
@@ -2,6 +2,7 @@ use crate::module::{MemoryPlan, MemoryStyle, Module, TableStyle};
 use crate::vmoffsets::VMOffsets;
 use crate::WASM_PAGE_SIZE;
 use cast;
+use core::clone::Clone;
 use cranelift_codegen::cursor::FuncCursor;
 use cranelift_codegen::ir;
 use cranelift_codegen::ir::condcodes::*;
@@ -16,7 +17,6 @@ use cranelift_wasm::{
     self, FuncIndex, GlobalIndex, GlobalVariable, MemoryIndex, SignatureIndex, TableIndex,
     WasmResult,
 };
-use std::clone::Clone;
 use std::vec::Vec;
 
 /// Compute an `ir::ExternalName` for a given wasm function index.
diff --git a/lib/environ/src/lib.rs b/lib/environ/src/lib.rs
index dc2a73f7fa..de119446c8 100644
--- a/lib/environ/src/lib.rs
+++ b/lib/environ/src/lib.rs
@@ -24,14 +24,23 @@
         clippy::use_self
     )
 )]
-#![cfg_attr(not(feature = "std"), no_std)]
+#![no_std]
 #![cfg_attr(not(feature = "std"), feature(alloc))]
 
-use cranelift_wasm;
 #[cfg(not(feature = "std"))]
 #[macro_use]
-extern crate alloc;
+extern crate alloc as std;
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
+#[cfg(not(feature = "std"))]
+use hashmap_core::HashMap;
+#[cfg(feature = "std")]
+use std::collections::HashMap;
+
 use cast;
+use cranelift_wasm;
 use failure;
 #[macro_use]
 extern crate failure_derive;
@@ -63,10 +72,3 @@ pub const WASM_PAGE_SIZE: u32 = 0x10000;
 
 /// The number of pages we can have before we run out of byte index space.
 pub const WASM_MAX_PAGES: u32 = 0x10000;
-
-#[cfg(not(feature = "std"))]
-mod std {
-    pub use alloc::{string, vec};
-    pub use core::*;
-    pub use core::{i32, str, u32};
-}
diff --git a/lib/environ/src/module.rs b/lib/environ/src/module.rs
index 6ed50d7f70..7d89118019 100644
--- a/lib/environ/src/module.rs
+++ b/lib/environ/src/module.rs
@@ -1,5 +1,6 @@
 //! Data structures for representing decoded wasm modules.
 
+use super::HashMap;
 use crate::tunables::Tunables;
 use cranelift_codegen::ir;
 use cranelift_entity::{EntityRef, PrimaryMap};
@@ -7,7 +8,6 @@ use cranelift_wasm::{
     DefinedFuncIndex, DefinedGlobalIndex, DefinedMemoryIndex, DefinedTableIndex, FuncIndex, Global,
     GlobalIndex, Memory, MemoryIndex, SignatureIndex, Table, TableIndex,
 };
-use std::collections::HashMap;
 use std::string::String;
 use std::vec::Vec;
 
diff --git a/lib/environ/src/module_environ.rs b/lib/environ/src/module_environ.rs
index 9971b32c6c..f3e92b7f25 100644
--- a/lib/environ/src/module_environ.rs
+++ b/lib/environ/src/module_environ.rs
@@ -1,6 +1,7 @@
 use crate::func_environ::FuncEnvironment;
 use crate::module::{Export, MemoryPlan, Module, TableElements, TablePlan};
 use crate::tunables::Tunables;
+use core::clone::Clone;
 use cranelift_codegen::ir;
 use cranelift_codegen::ir::{AbiParam, ArgumentPurpose};
 use cranelift_codegen::isa::TargetFrontendConfig;
@@ -9,7 +10,6 @@ use cranelift_wasm::{
     self, translate_module, DefinedFuncIndex, FuncIndex, Global, GlobalIndex, Memory, MemoryIndex,
     SignatureIndex, Table, TableIndex, WasmResult,
 };
-use std::clone::Clone;
 use std::string::String;
 use std::vec::Vec;
 
diff --git a/lib/jit/Cargo.toml b/lib/jit/Cargo.toml
index 46ce2cd100..194479d114 100644
--- a/lib/jit/Cargo.toml
+++ b/lib/jit/Cargo.toml
@@ -20,12 +20,13 @@ wasmtime-runtime = { path = "../runtime" }
 region = "1.0.0"
 failure = { version = "0.1.3", default-features = false }
 failure_derive = { version = "0.1.3", default-features = false }
-target-lexicon = "0.2.0"
+target-lexicon = { version = "0.2.0", default-features = false }
+hashmap_core = { version = "0.1.9", optional = true }
 
 [features]
 default = ["std"]
 std = ["cranelift-codegen/std", "cranelift-wasm/std"]
-core = ["cranelift-codegen/core", "cranelift-wasm/core", "wasmtime-environ/core"]
+core = ["hashmap_core", "cranelift-codegen/core", "cranelift-wasm/core", "wasmtime-environ/core"]
 
 [badges]
 maintenance = { status = "experimental" }
diff --git a/lib/jit/src/action.rs b/lib/jit/src/action.rs
index 3cf5024ed3..abbedde5e0 100644
--- a/lib/jit/src/action.rs
+++ b/lib/jit/src/action.rs
@@ -2,11 +2,11 @@
 
 use crate::compiler::Compiler;
 use crate::instantiate::SetupError;
+use core::cmp::max;
+use core::{fmt, mem, ptr, slice};
 use cranelift_codegen::ir;
-use std::cmp::max;
 use std::string::String;
 use std::vec::Vec;
-use std::{fmt, mem, ptr, slice};
 use wasmtime_runtime::{wasmtime_call_trampoline, Export, Instance};
 
 /// A runtime value.
diff --git a/lib/jit/src/code_memory.rs b/lib/jit/src/code_memory.rs
index 5374ad7800..5b24f4c768 100644
--- a/lib/jit/src/code_memory.rs
+++ b/lib/jit/src/code_memory.rs
@@ -1,9 +1,9 @@
 //! Memory management for executable code.
 
+use core::{cmp, mem};
 use region;
 use std::string::String;
 use std::vec::Vec;
-use std::{cmp, mem};
 use wasmtime_runtime::{Mmap, VMFunctionBody};
 
 /// Memory manager for executable code.
diff --git a/lib/jit/src/compiler.rs b/lib/jit/src/compiler.rs
index 1a3e0a2203..2fab3d5120 100644
--- a/lib/jit/src/compiler.rs
+++ b/lib/jit/src/compiler.rs
@@ -1,5 +1,6 @@
 //! JIT compilation.
 
+use super::HashMap;
 use crate::code_memory::CodeMemory;
 use crate::instantiate::SetupError;
 use crate::target_tunables::target_tunables;
@@ -11,7 +12,6 @@ use cranelift_entity::PrimaryMap;
 use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
 use cranelift_wasm::DefinedFuncIndex;
 use std::boxed::Box;
-use std::collections::HashMap;
 use std::string::String;
 use std::vec::Vec;
 use wasmtime_environ::cranelift;
@@ -95,7 +95,7 @@ impl Compiler {
         signature: &ir::Signature,
         value_size: usize,
     ) -> Result<*const VMFunctionBody, SetupError> {
-        use std::collections::hash_map::Entry::{Occupied, Vacant};
+        use super::hash_map::Entry::{Occupied, Vacant};
         Ok(match self.trampoline_park.entry(callee_address) {
             Occupied(entry) => *entry.get(),
             Vacant(entry) => {
diff --git a/lib/jit/src/lib.rs b/lib/jit/src/lib.rs
index 577fa6d71b..5c7eaf334b 100644
--- a/lib/jit/src/lib.rs
+++ b/lib/jit/src/lib.rs
@@ -21,18 +21,26 @@
         clippy::use_self
     )
 )]
-#![cfg_attr(not(feature = "std"), no_std)]
+#![no_std]
 #![cfg_attr(not(feature = "std"), feature(alloc))]
 
+#[cfg(not(feature = "std"))]
+#[macro_use]
+extern crate alloc as std;
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
+#[cfg(not(feature = "std"))]
+use hashmap_core::{map as hash_map, HashMap};
+#[cfg(feature = "std")]
+use std::collections::{hash_map, HashMap};
+
 #[macro_use]
 extern crate cranelift_entity;
 
-use region;
-
-#[cfg(not(feature = "std"))]
-#[macro_use]
-extern crate alloc;
 use failure;
+use region;
 
 #[macro_use]
 extern crate failure_derive;
@@ -57,10 +65,3 @@ pub use crate::target_tunables::target_tunables;
 // Re-export `Instance` so that users won't need to separately depend on
 // wasmtime-runtime in common cases.
 pub use wasmtime_runtime::{Instance, InstantiationError};
-
-#[cfg(not(feature = "std"))]
-mod std {
-    pub use alloc::{boxed, rc, string, vec};
-    pub use core::*;
-    pub use core::{i32, str, u32};
-}
diff --git a/lib/jit/src/link.rs b/lib/jit/src/link.rs
index 9cfdef857f..47c87c1960 100644
--- a/lib/jit/src/link.rs
+++ b/lib/jit/src/link.rs
@@ -1,10 +1,10 @@
 //! Linking for JIT-compiled code.
 
 use crate::resolver::Resolver;
+use core::ptr::write_unaligned;
 use cranelift_codegen::binemit::Reloc;
 use cranelift_entity::PrimaryMap;
 use cranelift_wasm::{DefinedFuncIndex, Global, GlobalInit, Memory, Table, TableElementType};
-use std::ptr::write_unaligned;
 use std::vec::Vec;
 use wasmtime_environ::{
     MemoryPlan, MemoryStyle, Module, Relocation, RelocationTarget, Relocations, TablePlan,
diff --git a/lib/jit/src/namespace.rs b/lib/jit/src/namespace.rs
index dda170f824..7794066eeb 100644
--- a/lib/jit/src/namespace.rs
+++ b/lib/jit/src/namespace.rs
@@ -2,12 +2,12 @@
 //! to exports. This file provides one possible way to manage multiple instances
 //! and resolve imports to exports among them.
 
+use super::HashMap;
 use crate::action::{get, inspect_memory, invoke};
 use crate::action::{ActionError, ActionOutcome, RuntimeValue};
 use crate::compiler::Compiler;
 use crate::resolver::Resolver;
 use cranelift_entity::PrimaryMap;
-use std::collections::HashMap;
 use std::string::String;
 use wasmtime_runtime::{Export, Instance};
 
diff --git a/lib/jit/src/target_tunables.rs b/lib/jit/src/target_tunables.rs
index 2fd5b4848f..dfeac9fbc7 100644
--- a/lib/jit/src/target_tunables.rs
+++ b/lib/jit/src/target_tunables.rs
@@ -1,4 +1,4 @@
-use std::cmp::min;
+use core::cmp::min;
 use target_lexicon::{OperatingSystem, Triple};
 use wasmtime_environ::Tunables;
 
diff --git a/lib/runtime/src/instance.rs b/lib/runtime/src/instance.rs
index 4959f3c67a..8fb8a36f90 100644
--- a/lib/runtime/src/instance.rs
+++ b/lib/runtime/src/instance.rs
@@ -13,16 +13,17 @@ use crate::vmcontext::{
     VMGlobalImport, VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex, VMTableDefinition,
     VMTableImport,
 };
+use core::slice;
+use core::{mem, ptr};
 use cranelift_entity::EntityRef;
 use cranelift_entity::{BoxedSlice, PrimaryMap};
 use cranelift_wasm::{
     DefinedFuncIndex, DefinedGlobalIndex, DefinedMemoryIndex, DefinedTableIndex, FuncIndex,
     GlobalIndex, GlobalInit, MemoryIndex, SignatureIndex, TableIndex,
 };
+use std::borrow::ToOwned;
 use std::rc::Rc;
-use std::slice;
 use std::string::String;
-use std::{mem, ptr};
 use wasmtime_environ::{DataInitializer, Module, TableElements, VMOffsets};
 
 fn signature_id(
diff --git a/lib/runtime/src/lib.rs b/lib/runtime/src/lib.rs
index 5086f654bd..9afcf725c1 100644
--- a/lib/runtime/src/lib.rs
+++ b/lib/runtime/src/lib.rs
@@ -21,15 +21,24 @@
         clippy::use_self
     )
 )]
-#![cfg_attr(not(feature = "std"), no_std)]
+#![no_std]
 #![cfg_attr(not(feature = "std"), feature(alloc))]
 
+#[cfg(not(feature = "std"))]
+#[macro_use]
+extern crate alloc as std;
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
+#[cfg(not(feature = "std"))]
+use hashmap_core::{map as hash_map, HashMap};
+#[cfg(feature = "std")]
+use std::collections::{hash_map, HashMap};
+
 use errno;
 use region;
 
-#[cfg(not(feature = "std"))]
-#[macro_use]
-extern crate alloc;
 #[macro_use]
 extern crate lazy_static;
 use libc;
@@ -66,10 +75,3 @@ pub use crate::vmcontext::{
     VMContext, VMFunctionBody, VMFunctionImport, VMGlobalDefinition, VMGlobalImport,
     VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex, VMTableDefinition, VMTableImport,
 };
-
-#[cfg(not(feature = "std"))]
-mod std {
-    pub use alloc::{string, vec};
-    pub use core::*;
-    pub use core::{i32, str, u32};
-}
diff --git a/lib/runtime/src/mmap.rs b/lib/runtime/src/mmap.rs
index fef3004ed3..cb11aedadb 100644
--- a/lib/runtime/src/mmap.rs
+++ b/lib/runtime/src/mmap.rs
@@ -1,12 +1,13 @@
 //! Low-level abstraction for allocating and managing zero-filled pages
 //! of memory.
 
+use core::ptr;
+use core::slice;
 use errno;
 use libc;
 use region;
-use std::ptr;
-use std::slice;
-use std::string::String;
+use std::string::{String, ToString};
+use std::vec::Vec;
 
 /// Round `size` up to the nearest multiple of `page_size`.
 fn round_up_to_page_size(size: usize, page_size: usize) -> usize {
diff --git a/lib/runtime/src/sig_registry.rs b/lib/runtime/src/sig_registry.rs
index 73d8cf1439..79a175a5e8 100644
--- a/lib/runtime/src/sig_registry.rs
+++ b/lib/runtime/src/sig_registry.rs
@@ -1,10 +1,10 @@
 //! Implement a registry of function signatures, for fast indirect call
 //! signature checking.
 
+use super::{hash_map, HashMap};
 use crate::vmcontext::VMSharedSignatureIndex;
 use cast;
 use cranelift_codegen::ir;
-use std::collections::{hash_map, HashMap};
 
 /// WebAssembly requires that the caller and callee signatures in an indirect
 /// call must match. To implement this efficiently, keep a registry of all
diff --git a/lib/runtime/src/signalhandlers.rs b/lib/runtime/src/signalhandlers.rs
index ddbc8d3ecf..3a4a052969 100644
--- a/lib/runtime/src/signalhandlers.rs
+++ b/lib/runtime/src/signalhandlers.rs
@@ -5,8 +5,8 @@
 #![allow(non_snake_case)]
 
 use crate::vmcontext::VMContext;
-use std::borrow::{Borrow, BorrowMut};
-use std::cell::RefCell;
+use core::borrow::{Borrow, BorrowMut};
+use core::cell::RefCell;
 use std::sync::RwLock;
 
 include!(concat!(env!("OUT_DIR"), "/signalhandlers.rs"));
diff --git a/lib/runtime/src/table.rs b/lib/runtime/src/table.rs
index 5665445b19..62c6f5db36 100644
--- a/lib/runtime/src/table.rs
+++ b/lib/runtime/src/table.rs
@@ -4,6 +4,7 @@
 
 use crate::vmcontext::{VMCallerCheckedAnyfunc, VMTableDefinition};
 use cranelift_wasm::TableElementType;
+use std::vec::Vec;
 use wasmtime_environ::{TablePlan, TableStyle};
 
 /// A table instance.
diff --git a/lib/runtime/src/traphandlers.rs b/lib/runtime/src/traphandlers.rs
index d3b34ee2f0..3339320c09 100644
--- a/lib/runtime/src/traphandlers.rs
+++ b/lib/runtime/src/traphandlers.rs
@@ -3,11 +3,12 @@
 
 use crate::signalhandlers::jmp_buf;
 use crate::vmcontext::{VMContext, VMFunctionBody};
+use core::cell::{Cell, RefCell};
+use core::mem;
+use core::ptr;
 use libc::c_int;
-use std::cell::{Cell, RefCell};
-use std::mem;
-use std::ptr;
 use std::string::String;
+use std::vec::Vec;
 
 // Currently we uset setjmp/longjmp to unwind out of a signal handler
 // and back to the point where WebAssembly was called (via `call_wasm`).
diff --git a/lib/runtime/src/vmcontext.rs b/lib/runtime/src/vmcontext.rs
index 03013b4c9c..3d8780e170 100644
--- a/lib/runtime/src/vmcontext.rs
+++ b/lib/runtime/src/vmcontext.rs
@@ -2,7 +2,7 @@
 //! fields that compiled wasm code accesses directly.
 
 use crate::instance::InstanceContents;
-use std::{ptr, u32};
+use core::{ptr, u32};
 
 /// An imported function.
 #[derive(Debug, Copy, Clone)]
@@ -18,7 +18,7 @@ pub struct VMFunctionImport {
 #[cfg(test)]
 mod test_vmfunction_import {
     use super::VMFunctionImport;
-    use std::mem::size_of;
+    use core::mem::size_of;
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]
@@ -50,7 +50,7 @@ pub struct VMFunctionBody(u8);
 #[cfg(test)]
 mod test_vmfunction_body {
     use super::VMFunctionBody;
-    use std::mem::size_of;
+    use core::mem::size_of;
 
     #[test]
     fn check_vmfunction_body_offsets() {
@@ -73,7 +73,7 @@ pub struct VMTableImport {
 #[cfg(test)]
 mod test_vmtable_import {
     use super::VMTableImport;
-    use std::mem::size_of;
+    use core::mem::size_of;
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]
@@ -110,7 +110,7 @@ pub struct VMMemoryImport {
 #[cfg(test)]
 mod test_vmmemory_import {
     use super::VMMemoryImport;
-    use std::mem::size_of;
+    use core::mem::size_of;
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]
@@ -144,7 +144,7 @@ pub struct VMGlobalImport {
 #[cfg(test)]
 mod test_vmglobal_import {
     use super::VMGlobalImport;
-    use std::mem::size_of;
+    use core::mem::size_of;
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]
@@ -178,7 +178,7 @@ pub struct VMMemoryDefinition {
 #[cfg(test)]
 mod test_vmmemory_definition {
     use super::VMMemoryDefinition;
-    use std::mem::size_of;
+    use core::mem::size_of;
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]
@@ -221,7 +221,7 @@ pub struct VMTableDefinition {
 #[cfg(test)]
 mod test_vmtable_definition {
     use super::VMTableDefinition;
-    use std::mem::size_of;
+    use core::mem::size_of;
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]
@@ -257,7 +257,7 @@ pub struct VMGlobalDefinition {
 #[cfg(test)]
 mod test_vmglobal_definition {
     use super::VMGlobalDefinition;
-    use std::mem::{align_of, size_of};
+    use core::mem::{align_of, size_of};
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]
@@ -391,7 +391,7 @@ pub struct VMSharedSignatureIndex(u32);
 #[cfg(test)]
 mod test_vmshared_signature_index {
     use super::VMSharedSignatureIndex;
-    use std::mem::size_of;
+    use core::mem::size_of;
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]
@@ -427,7 +427,7 @@ pub struct VMCallerCheckedAnyfunc {
 #[cfg(test)]
 mod test_vmcaller_checked_anyfunc {
     use super::VMCallerCheckedAnyfunc;
-    use std::mem::size_of;
+    use core::mem::size_of;
     use wasmtime_environ::{Module, VMOffsets};
 
     #[test]