diff --git a/pkg/dart2wasm/dart2wasm.md b/pkg/dart2wasm/dart2wasm.md
index 0f9d65f9e7c..dd96ed20459 100644
--- a/pkg/dart2wasm/dart2wasm.md
+++ b/pkg/dart2wasm/dart2wasm.md
@@ -60,5 +60,5 @@ inst.exports.baz(2);
 In the signatures of imported and exported functions, use the following types:
 
 - For numbers, use `double`.
-- For Dart objects, use the corresponding Dart type. The fields of the underlying representation can be accessed on the JS side as `.$field0`, `.$field1` etc., but there is currently no defined way of finding the field index of a particular Dart field, so this mechanism is mainly useful for special objects with known layout.
-- For JS objects, use the `WasmAnyRef` type (or `WasmAnyRef?` as applicable) from the `dart:wasm` package. These can be passed around and stored as opaque values on the Dart side.
+- For JS objects, use the `WasmExternRef?` type from the `dart:wasm` package, which translates to the Wasm `externref` type. These can be passed around and stored as opaque values on the Dart side.
+- For Dart objects, use the corresponding Dart type. This will be emitted as `externref` and automatically converted to and from the Dart type at the boundary.
diff --git a/pkg/dart2wasm/lib/code_generator.dart b/pkg/dart2wasm/lib/code_generator.dart
index d96f90c1469..9a282f58245 100644
--- a/pkg/dart2wasm/lib/code_generator.dart
+++ b/pkg/dart2wasm/lib/code_generator.dart
@@ -333,6 +333,22 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
       typeLocals[typeParameters[i]] = paramLocals[typeParameterOffset + i];
     }
 
+    // For all parameters whose Wasm type has been forced to `externref` due to
+    // this function being an export, internalize and cast the parameter to the
+    // canonical representation type for its Dart type.
+    locals.forEach((parameter, local) {
+      DartType parameterType = parameter.type;
+      if (local.type == w.RefType.extern(nullable: true) &&
+          !(parameterType is InterfaceType &&
+              parameterType.classNode == translator.wasmExternRefClass)) {
+        w.Local newLocal = addLocal(translateType(parameterType));
+        b.local_get(local);
+        translator.convertType(function, local.type, newLocal.type);
+        b.local_set(newLocal);
+        locals[parameter] = newLocal;
+      }
+    });
+
     closures.findCaptures(member);
 
     if (hasThis) {
@@ -1408,7 +1424,7 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
 
   @override
   w.ValueType visitEqualsNull(EqualsNull node, w.ValueType expectedType) {
-    wrap(node.expression, const w.RefType.top(nullable: true));
+    wrap(node.expression, const w.RefType.any(nullable: true));
     b.ref_is_null();
     return w.NumType.i32;
   }
diff --git a/pkg/dart2wasm/lib/functions.dart b/pkg/dart2wasm/lib/functions.dart
index 10bdcd588d3..dfe61897432 100644
--- a/pkg/dart2wasm/lib/functions.dart
+++ b/pkg/dart2wasm/lib/functions.dart
@@ -219,12 +219,14 @@ class FunctionCollector extends MemberVisitor1<w.FunctionType, Reference> {
     List<w.ValueType> typeParameters = List.filled(typeParamCount,
         translator.classInfo[translator.typeClass]!.nonNullableType);
 
-    // The JS embedder will not accept Wasm struct types as parameter or return
-    // types for functions called from JS. We need to use eqref instead.
+    // The only reference types allowed as parameters and returns on imported
+    // or exported functions for JS interop are `externref` and `funcref`.
     w.ValueType adjustExternalType(w.ValueType type) {
-      if (isImportOrExport &&
-          type.isSubtypeOf(translator.topInfo.nullableType)) {
-        return w.RefType.eq(nullable: type.nullable);
+      if (isImportOrExport && type is w.RefType) {
+        if (type.heapType.isSubtypeOf(w.HeapType.func)) {
+          return w.RefType.func(nullable: true);
+        }
+        return w.RefType.extern(nullable: true);
       }
       return type;
     }
diff --git a/pkg/dart2wasm/lib/translator.dart b/pkg/dart2wasm/lib/translator.dart
index a03e359cb84..d1b1ef82806 100644
--- a/pkg/dart2wasm/lib/translator.dart
+++ b/pkg/dart2wasm/lib/translator.dart
@@ -739,8 +739,8 @@ class Translator {
       }
       if (to != voidMarker) {
         if (to is w.RefType && to.nullable) {
-          // This can happen when a void method has its return type overridden to
-          // return a value, in which case the selector signature will have a
+          // This can happen when a void method has its return type overridden
+          // to return a value, in which case the selector signature will have a
           // non-void return type to encompass all possible return values.
           b.ref_null(to.heapType);
         } else {
@@ -752,6 +752,17 @@ class Translator {
         return;
       }
     }
+
+    bool fromIsExtern = from.isSubtypeOf(w.RefType.extern(nullable: true));
+    bool toIsExtern = to.isSubtypeOf(w.RefType.extern(nullable: true));
+    if (fromIsExtern && !toIsExtern) {
+      b.extern_internalize();
+      from = w.RefType.any(nullable: from.nullable);
+    }
+    if (!fromIsExtern && toIsExtern) {
+      to = w.RefType.any(nullable: to.nullable);
+    }
+
     if (!from.isSubtypeOf(to)) {
       if (from is! w.RefType && to is w.RefType) {
         // Boxing
@@ -812,6 +823,10 @@ class Translator {
         }
       }
     }
+
+    if (!fromIsExtern && toIsExtern) {
+      b.extern_externalize();
+    }
   }
 
   w.FunctionType signatureFor(Reference target) {
diff --git a/sdk/lib/_internal/wasm/lib/async_patch.dart b/sdk/lib/_internal/wasm/lib/async_patch.dart
index e9ed97eaf70..b9e3dfb6a2a 100644
--- a/sdk/lib/_internal/wasm/lib/async_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/async_patch.dart
@@ -53,20 +53,18 @@ import 'dart:_internal' show patch, scheduleCallback, unsafeCastOpaque;
 import 'dart:wasm';
 
 @pragma("wasm:entry-point")
-Future<T> _asyncHelper<T>(WasmEqRef args) {
+Future<T> _asyncHelper<T>(WasmDataRef args) {
   Completer<T> completer = Completer();
   _callAsyncBridge(args, completer);
   return completer.future;
 }
 
 @pragma("wasm:import", "dart2wasm.callAsyncBridge")
-external void _callAsyncBridge(WasmEqRef args, Completer<Object?> completer);
+external void _callAsyncBridge(WasmDataRef args, Completer<Object?> completer);
 
 @pragma("wasm:export", "\$asyncBridge")
 WasmAnyRef? _asyncBridge(
-    WasmExternRef? stack, WasmExternRef? argsRef, WasmExternRef? completerRef) {
-  WasmDataRef args = unsafeCastOpaque(argsRef!.internalize());
-  Completer<Object?> completer = unsafeCastOpaque(completerRef!.internalize());
+    WasmExternRef? stack, WasmDataRef args, Completer<Object?> completer) {
   try {
     Object? result = _asyncBridge2(args, stack);
     completer.complete(result);
@@ -87,9 +85,7 @@ class _FutureError {
 @pragma("wasm:entry-point")
 Object? _awaitHelper(Object? operand, WasmExternRef? stack) {
   if (operand is! Future) return operand;
-  WasmExternRef futureRef = WasmAnyRef.fromObject(operand).externalize();
-  Object? result =
-      unsafeCastOpaque(_futurePromise(stack, futureRef).internalize());
+  Object? result = _futurePromise(stack, operand);
   if (result is _FutureError) {
     // TODO(askesc): Combine stack traces
     throw result.exception;
@@ -98,11 +94,10 @@ Object? _awaitHelper(Object? operand, WasmExternRef? stack) {
 }
 
 @pragma("wasm:import", "dart2wasm.futurePromise")
-external WasmExternRef? _futurePromise(
-    WasmExternRef? stack, WasmExternRef? future);
+external Object? _futurePromise(WasmExternRef? stack, Future<Object?> future);
 
 @pragma("wasm:export", "\$awaitCallback")
-void _awaitCallback(Future<Object?> future, WasmAnyRef resolve) {
+void _awaitCallback(Future<Object?> future, WasmExternRef? resolve) {
   future.then((value) {
     _callResolve(resolve, value);
   }, onError: (exception, stackTrace) {
@@ -111,4 +106,4 @@ void _awaitCallback(Future<Object?> future, WasmAnyRef resolve) {
 }
 
 @pragma("wasm:import", "dart2wasm.callResolve")
-external void _callResolve(WasmAnyRef resolve, Object? result);
+external void _callResolve(WasmExternRef? resolve, Object? result);
diff --git a/tests/web/wasm/wasm_types_test.dart b/tests/web/wasm/wasm_types_test.dart
index 0ce54a34b58..1f1da18b621 100644
--- a/tests/web/wasm/wasm_types_test.dart
+++ b/tests/web/wasm/wasm_types_test.dart
@@ -7,14 +7,14 @@ import 'dart:wasm';
 import 'package:expect/expect.dart';
 
 @pragma("wasm:import", "Object.create")
-external WasmAnyRef createObject(WasmAnyRef? prototype);
+external WasmExternRef? createObject(WasmExternRef? prototype);
 
 @pragma("wasm:import", "Array.of")
-external WasmAnyRef singularArray(WasmAnyRef element);
+external WasmExternRef? singularArray(WasmExternRef? element);
 
 @pragma("wasm:import", "Reflect.apply")
-external WasmAnyRef apply(
-    WasmFuncRef target, WasmAnyRef thisArgument, WasmAnyRef argumentsList);
+external WasmExternRef? apply(WasmFuncRef? target, WasmExternRef? thisArgument,
+    WasmExternRef? argumentsList);
 
 WasmAnyRef? anyRef;
 WasmEqRef? eqRef;
@@ -32,7 +32,7 @@ test() {
   Object dartObject1 = "1";
   Object dartObject2 = true;
   Object dartObject3 = Object();
-  WasmAnyRef jsObject1 = createObject(null);
+  WasmAnyRef jsObject1 = createObject(null)!.internalize();
 
   // A JS object is not a Dart object.
   Expect.isFalse(jsObject1.isObject);
@@ -77,7 +77,7 @@ test() {
   var dartObjectRef = WasmEqRef.fromObject("Dart object");
   var ff = WasmFunction.fromFunction(fun);
   ff.call(dartObjectRef);
-  apply(ff, createObject(null), singularArray(dartObjectRef));
+  apply(ff, createObject(null), singularArray(dartObjectRef.externalize()));
 
   // Cast a typed function reference to a `funcref` and back.
   WasmFuncRef funcref = WasmFuncRef.fromWasmFunction(ff);
@@ -86,7 +86,7 @@ test() {
 
   // Create a typed function reference from an import and call it.
   var createObjectFun = WasmFunction.fromFunction(createObject);
-  WasmAnyRef jsObject3 = createObjectFun.call(null);
+  WasmAnyRef jsObject3 = createObjectFun.call(null).internalize()!;
   Expect.isFalse(jsObject3.isObject);
 
   Expect.equals(3, funCount);