diff --git a/lib/environ/src/module_environ.rs b/lib/environ/src/module_environ.rs
index 763258e56c..1a75d21e45 100644
--- a/lib/environ/src/module_environ.rs
+++ b/lib/environ/src/module_environ.rs
@@ -160,6 +160,9 @@ impl<'data> cranelift_wasm::ModuleEnvironment<'data> for ModuleEnvironment<'data
 
     fn reserve_func_types(&mut self, num: u32) {
         self.result.module.functions.reserve_exact(cast::usize(num));
+        self.result
+            .function_body_inputs
+            .reserve_exact(cast::usize(num));
     }
 
     fn declare_func_type(&mut self, sig_index: SignatureIndex) {
diff --git a/lib/jit/src/compiler.rs b/lib/jit/src/compiler.rs
index 54359ea9cc..f7b94d3f11 100644
--- a/lib/jit/src/compiler.rs
+++ b/lib/jit/src/compiler.rs
@@ -154,7 +154,6 @@ fn make_trampoline(
         builder.switch_to_block(block0);
         builder.seal_block(block0);
 
-        let mut callee_args = Vec::new();
         let (vmctx_ptr_val, values_vec_ptr_val) = {
             let params = builder.func.dfg.ebb_params(block0);
             (params[0], params[1])
@@ -162,20 +161,24 @@ fn make_trampoline(
 
         // Load the argument values out of `values_vec`.
         let mflags = ir::MemFlags::trusted();
-        for (i, r) in signature.params.iter().enumerate() {
-            let value = match r.purpose {
-                // i - 1 because vmctx isn't passed through `values_vec`.
-                ir::ArgumentPurpose::Normal => builder.ins().load(
-                    r.value_type,
-                    mflags,
-                    values_vec_ptr_val,
-                    ((i - 1) * value_size) as i32,
-                ),
-                ir::ArgumentPurpose::VMContext => vmctx_ptr_val,
-                other => panic!("unsupported argument purpose {}", other),
-            };
-            callee_args.push(value);
-        }
+        let callee_args = signature
+            .params
+            .iter()
+            .enumerate()
+            .map(|(i, r)| {
+                match r.purpose {
+                    // i - 1 because vmctx isn't passed through `values_vec`.
+                    ir::ArgumentPurpose::Normal => builder.ins().load(
+                        r.value_type,
+                        mflags,
+                        values_vec_ptr_val,
+                        ((i - 1) * value_size) as i32,
+                    ),
+                    ir::ArgumentPurpose::VMContext => vmctx_ptr_val,
+                    other => panic!("unsupported argument purpose {}", other),
+                }
+            })
+            .collect::<Vec<_>>();
 
         let new_sig = builder.import_signature(signature.clone());
 
diff --git a/lib/jit/src/instantiate.rs b/lib/jit/src/instantiate.rs
index 076a4ab472..1dd46679a9 100644
--- a/lib/jit/src/instantiate.rs
+++ b/lib/jit/src/instantiate.rs
@@ -87,11 +87,12 @@ impl<'data> RawCompiledModule<'data> {
         // Compute indices into the shared signature table.
         let signatures = {
             let signature_registry = compiler.signatures();
-            let mut signatures = PrimaryMap::new();
-            for sig in translation.module.signatures.values() {
-                signatures.push(signature_registry.register(sig));
-            }
-            signatures
+            translation
+                .module
+                .signatures
+                .values()
+                .map(|sig| signature_registry.register(sig))
+                .collect::<PrimaryMap<_, _>>()
         };
 
         // Make all code compiled thus far executable.