diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/CancelablePromise.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/CancelablePromise.cs
index 391f692e0baf08..45e23cf2e48111 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/CancelablePromise.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/CancelablePromise.cs
@@ -21,6 +21,15 @@ public static void CancelPromise(Task promise)
             GCHandle? promiseGCHandle = promise.AsyncState as GCHandle?;
             if (promiseGCHandle == null) throw new InvalidOperationException("Expected Task converted from JS Promise");
 
+#if FEATURE_WASM_THREADS
+            // TODO JSObject.AssertThreadAffinity(promise);
+            // in order to remember the thread ID of the promise, we would have to allocate holder object for any Task,
+            // which would hold thread ID and the GCHandle
+            // that would be pretty expensive, so we don't do it for now
+            // the consequences are that calling CancelPromise on wrong thread would do nothing
+            // because there would not be any object on JS registered under the same GCHandle
+            // perhaps that's the point when we could throw an exception on JS side.
+#endif
             _CancelPromise((IntPtr)promiseGCHandle.Value);
         }
     }
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Interop/LegacyExports.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Interop/LegacyExports.cs
index 10092d5971bb4f..38605743fad931 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Interop/LegacyExports.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Interop/LegacyExports.cs
@@ -71,6 +71,10 @@ public static IntPtr TryGetCSOwnedObjectJSHandleRef(in object rawObj, int should
 
         public static void CreateCSOwnedProxyRef(nint jsHandle, LegacyHostImplementation.MappedType mappedType, int shouldAddInflight, out JSObject jsObject)
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
+
             JSObject? res = null;
 
             lock (JSHostImplementation.s_csOwnedObjects)
@@ -144,6 +148,9 @@ public static void GetTaskSourceTaskRef(int tcsGCHandle, out object result)
 
         public static void SetupJSContinuationRef(in Task _task, JSObject continuationObj)
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             // HACK: Attempting to use the in-param will produce CS1628, so we make a temporary copy
             //  on the stack that can be captured by our local functions below
             var task = _task;
@@ -225,6 +232,9 @@ public static void CreateDateTimeRef(double ticks, out object result)
         [Diagnostics.CodeAnalysis.UnconditionalSuppressMessage("Trimming", "IL2057", Justification = "Done on purpose, see comment above.")]
         public static void CreateUriRef(string uri, out object? result)
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             if (uriType == null)
             {
                 // StringBuilder to confuse ILLink, which is too smart otherwise
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSFunctionBinding.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSFunctionBinding.cs
index c01965dc4610c3..8d415f7201e5c4 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSFunctionBinding.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSFunctionBinding.cs
@@ -172,6 +172,10 @@ public static JSFunctionBinding BindManagedFunction(string fullyQualifiedName, i
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static unsafe void InvokeJSImpl(JSObject jsFunction, Span<JSMarshalerArgument> arguments)
         {
+#if FEATURE_WASM_THREADS
+            JSObject.AssertThreadAffinity(jsFunction);
+#endif
+
             IntPtr functionJSHandle = jsFunction.JSHandle;
             fixed (JSMarshalerArgument* ptr = arguments)
             {
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSObject.References.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSObject.References.cs
index d731a48392b1e1..6cc22a1f254e65 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSObject.References.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSObject.References.cs
@@ -3,6 +3,7 @@
 
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
+using System.Threading;
 
 namespace System.Runtime.InteropServices.JavaScript
 {
@@ -10,6 +11,10 @@ public partial class JSObject
     {
         internal nint JSHandle;
 
+#if FEATURE_WASM_THREADS
+        // the JavaScript object could only exist on the single web worker and can't migrate to other workers
+        internal int OwnerThreadId;
+#endif
 #if !DISABLE_LEGACY_JS_INTEROP
         internal GCHandle? InFlight;
         internal int InFlightCounter;
@@ -19,6 +24,9 @@ public partial class JSObject
         internal JSObject(IntPtr jsHandle)
         {
             JSHandle = jsHandle;
+#if FEATURE_WASM_THREADS
+            OwnerThreadId = Thread.CurrentThread.ManagedThreadId;
+#endif
         }
 
 #if !DISABLE_LEGACY_JS_INTEROP
@@ -56,6 +64,30 @@ internal void ReleaseInFlight()
         }
 #endif
 
+#if FEATURE_WASM_THREADS
+        internal static void AssertThreadAffinity(object value)
+        {
+            if (value == null)
+            {
+                return;
+            }
+            if (value is JSObject jsObject)
+            {
+                if (jsObject.OwnerThreadId != Thread.CurrentThread.ManagedThreadId)
+                {
+                    throw new InvalidOperationException("The JavaScript object can be used only on the thread where it was created.");
+                }
+            }
+            if (value is JSException jsException)
+            {
+                if(jsException.jsException!=null && jsException.jsException.OwnerThreadId != Thread.CurrentThread.ManagedThreadId)
+                {
+                    throw new InvalidOperationException("The JavaScript object can be used only on the thread where it was created.");
+                }
+            }
+        }
+#endif
+
         /// <inheritdoc />
         public override bool Equals([NotNullWhen(true)] object? obj) => obj is JSObject other && JSHandle == other.JSHandle;
 
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Array.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Array.cs
index 987a2d2fd8bf0c..29ada438164ccf 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Array.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Array.cs
@@ -18,6 +18,9 @@ public class Array : JSObject
         public Array(params object[] _params)
             : base(JavaScriptImports.CreateCSOwnedObject(nameof(Array), _params))
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             LegacyHostImplementation.RegisterCSOwnedObject(this);
         }
 
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/ArrayBuffer.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/ArrayBuffer.cs
index e19dd5ffc6df8a..39db0563089d0d 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/ArrayBuffer.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/ArrayBuffer.cs
@@ -13,6 +13,9 @@ public class ArrayBuffer : JSObject
         public ArrayBuffer(int length)
             : base(JavaScriptImports.CreateCSOwnedObject(nameof(ArrayBuffer), new object[] { length }))
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             LegacyHostImplementation.RegisterCSOwnedObject(this);
         }
 
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/DataView.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/DataView.cs
index f43583e512a180..3d3300ec5c5039 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/DataView.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/DataView.cs
@@ -17,6 +17,9 @@ public class DataView : JSObject
         public DataView(ArrayBuffer buffer)
             : base(JavaScriptImports.CreateCSOwnedObject(nameof(DataView), new object[] { buffer }))
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             LegacyHostImplementation.RegisterCSOwnedObject(this);
         }
 
@@ -28,6 +31,9 @@ public DataView(ArrayBuffer buffer)
         public DataView(ArrayBuffer buffer, int byteOffset)
             : base(JavaScriptImports.CreateCSOwnedObject(nameof(DataView), new object[] { buffer, byteOffset }))
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             LegacyHostImplementation.RegisterCSOwnedObject(this);
         }
 
@@ -40,6 +46,9 @@ public DataView(ArrayBuffer buffer, int byteOffset)
         public DataView(ArrayBuffer buffer, int byteOffset, int byteLength)
             : base(JavaScriptImports.CreateCSOwnedObject(nameof(DataView), new object[] { buffer, byteOffset, byteLength }))
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             LegacyHostImplementation.RegisterCSOwnedObject(this);
         }
 
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Function.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Function.cs
index 2c778706b497e1..f87fb94c01610a 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Function.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Function.cs
@@ -18,6 +18,9 @@ public class Function : JSObject
         public Function(params object[] args)
             : base(JavaScriptImports.CreateCSOwnedObject(nameof(Function), args))
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             LegacyHostImplementation.RegisterCSOwnedObject(this);
         }
 
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/LegacyHostImplementation.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/LegacyHostImplementation.cs
index d24a1decdff638..6a5de6a03e5038 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/LegacyHostImplementation.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/LegacyHostImplementation.cs
@@ -4,6 +4,7 @@
 using System.Runtime.CompilerServices;
 using System.Runtime.Versioning;
 using System.Threading.Tasks;
+using System.Threading;
 
 namespace System.Runtime.InteropServices.JavaScript
 {
@@ -220,5 +221,15 @@ public enum MappedType
             Function = 4,
             Uint8Array = 11,
         }
+
+#if FEATURE_WASM_THREADS
+        public static void ThrowIfLegacyWorkerThread()
+        {
+            if (Thread.CurrentThread.ManagedThreadId != 1)
+            {
+                throw new PlatformNotSupportedException("Legacy interop is not supported with WebAssembly threads.");
+            }
+        }
+#endif
     }
 }
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Runtime.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Runtime.cs
index 13147c81020525..c6e0e362af65e7 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Runtime.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Runtime.cs
@@ -34,6 +34,9 @@ public static object GetGlobalObject(string str)
         /// </returns>
         public static object Invoke(this JSObject self, string method, params object?[] args)
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             ArgumentNullException.ThrowIfNull(self);
             ObjectDisposedException.ThrowIf(self.IsDisposed, self);
             Interop.Runtime.InvokeJSWithArgsRef(self.JSHandle, method, args, out int exception, out object res);
@@ -68,6 +71,9 @@ public static object Invoke(this JSObject self, string method, params object?[]
         /// </returns>
         public static object GetObjectProperty(this JSObject self, string name)
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             ArgumentNullException.ThrowIfNull(self);
             ObjectDisposedException.ThrowIf(self.IsDisposed, self);
 
@@ -92,6 +98,9 @@ public static object GetObjectProperty(this JSObject self, string name)
         /// <param name="hasOwnProperty"></param>
         public static void SetObjectProperty(this JSObject self, string name, object? value, bool createIfNotExists = true, bool hasOwnProperty = false)
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             ArgumentNullException.ThrowIfNull(self);
             ObjectDisposedException.ThrowIf(self.IsDisposed, self);
 
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Uint8Array.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Uint8Array.cs
index fb9c8dae9539dc..b80f7c31ad64b4 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Uint8Array.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Legacy/Uint8Array.cs
@@ -11,12 +11,18 @@ public sealed class Uint8Array : JSObject
         public Uint8Array(int length)
             : base(JavaScriptImports.CreateCSOwnedObject(nameof(Uint8Array), new object[] { length }))
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             LegacyHostImplementation.RegisterCSOwnedObject(this);
         }
 
         public Uint8Array(ArrayBuffer buffer)
             : base(JavaScriptImports.CreateCSOwnedObject(nameof(Uint8Array), new object[] { buffer }))
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             LegacyHostImplementation.RegisterCSOwnedObject(this);
         }
 
@@ -49,6 +55,9 @@ public byte[] ToArray()
 
         public static unsafe Uint8Array From(ReadOnlySpan<byte> span)
         {
+#if FEATURE_WASM_THREADS
+            LegacyHostImplementation.ThrowIfLegacyWorkerThread();
+#endif
             // source has to be instantiated.
             if (span == null)
             {
@@ -65,7 +74,6 @@ public static unsafe Uint8Array From(ReadOnlySpan<byte> span)
                 r.ReleaseInFlight();
                 return r;
             }
-
         }
 
         public enum TypedArrayTypeCode
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Exception.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Exception.cs
index d847549a4a59d1..e19a3f428c8a23 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Exception.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Exception.cs
@@ -65,6 +65,9 @@ public unsafe void ToJS(Exception? value)
                 var jse = cpy as JSException;
                 if (jse != null && jse.jsException != null)
                 {
+#if FEATURE_WASM_THREADS
+                    JSObject.AssertThreadAffinity(value);
+#endif
                     // this is JSException roundtrip
                     ObjectDisposedException.ThrowIf(jse.jsException.IsDisposed, value);
                     slot.Type = MarshalerType.JSException;
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.JSObject.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.JSObject.cs
index 2e9f155f3f75be..5717e8d2cee87a 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.JSObject.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.JSObject.cs
@@ -37,6 +37,9 @@ public void ToJS(JSObject? value)
             }
             else
             {
+#if FEATURE_WASM_THREADS
+                JSObject.AssertThreadAffinity(value);
+#endif
                 ObjectDisposedException.ThrowIf(value.IsDisposed, value);
                 slot.Type = MarshalerType.JSObject;
                 slot.JSHandle = value.JSHandle;
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Task.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Task.cs
index 7d8d37b04c0269..3ebd4d7618fa47 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Task.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Task.cs
@@ -228,6 +228,10 @@ public void ToJS(Task? value)
 
             void Complete()
             {
+#if FEATURE_WASM_THREADS
+                JSObject.AssertThreadAffinity(promise);
+#endif
+
                 // When this task was never resolved/rejected
                 // promise (held by this lambda) would be collected by GC after the Task is collected
                 // and would also allow the JS promise to be collected
@@ -304,6 +308,9 @@ public void ToJS<T>(Task<T>? value, ArgumentToJSCallback<T> marshaler)
 
             void Complete()
             {
+#if FEATURE_WASM_THREADS
+                JSObject.AssertThreadAffinity(promise);
+#endif
                 // When this task was never resolved/rejected
                 // promise (held by this lambda) would be collected by GC after the Task is collected
                 // and would also allow the JS promise to be collected
diff --git a/src/mono/wasm/runtime/net6-legacy/method-binding.ts b/src/mono/wasm/runtime/net6-legacy/method-binding.ts
index 2eefa077fa2c56..a5614e2e82dc7b 100644
--- a/src/mono/wasm/runtime/net6-legacy/method-binding.ts
+++ b/src/mono/wasm/runtime/net6-legacy/method-binding.ts
@@ -1,8 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+import MonoWasmThreads from "consts:monoWasmThreads";
 import { legacy_c_functions as cwraps } from "../cwraps";
-import { Module } from "../imports";
+import { ENVIRONMENT_IS_PTHREAD, Module } from "../imports";
 import { parseFQN } from "../invoke-cs";
 import { setI32, setU32, setF32, setF64, setU52, setI52, setB32, setI32_unchecked, setU32_unchecked, _zero_region, _create_temp_frame, getB32, getI32, getU32, getF32, getF64 } from "../memory";
 import { mono_wasm_new_external_root, mono_wasm_new_root } from "../roots";
@@ -382,6 +383,9 @@ export function _decide_if_result_is_marshaled(converter: Converter, argc: numbe
 
 
 export function mono_bind_method(method: MonoMethod, args_marshal: string/*ArgsMarshalString*/, has_this_arg: boolean, friendly_name?: string): Function {
+    if (MonoWasmThreads && ENVIRONMENT_IS_PTHREAD) {
+        throw new Error("Legacy interop is not supported with WebAssembly threads.");
+    }
     if (typeof (args_marshal) !== "string")
         throw new Error("args_marshal argument invalid, expected string");
 
diff --git a/src/mono/wasm/runtime/net6-legacy/method-calls.ts b/src/mono/wasm/runtime/net6-legacy/method-calls.ts
index f1a89755eb5c1f..fa50cb01d42416 100644
--- a/src/mono/wasm/runtime/net6-legacy/method-calls.ts
+++ b/src/mono/wasm/runtime/net6-legacy/method-calls.ts
@@ -1,8 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+import MonoWasmThreads from "consts:monoWasmThreads";
 import { get_js_obj, mono_wasm_get_jsobj_from_js_handle } from "../gc-handles";
-import { Module, runtimeHelpers, INTERNAL } from "../imports";
+import { Module, runtimeHelpers, INTERNAL, ENVIRONMENT_IS_PTHREAD } from "../imports";
 import { wrap_error_root, wrap_no_error_root } from "../invoke-js";
 import { _release_temp_frame } from "../memory";
 import { mono_wasm_new_external_root, mono_wasm_new_root } from "../roots";
@@ -90,6 +91,9 @@ export function mono_call_assembly_entry_point(assembly: string, args?: any[], s
 }
 
 export function mono_wasm_invoke_js_with_args_ref(js_handle: JSHandle, method_name: MonoStringRef, args: MonoObjectRef, is_exception: Int32Ptr, result_address: MonoObjectRef): any {
+    if (MonoWasmThreads && ENVIRONMENT_IS_PTHREAD) {
+        throw new Error("Legacy interop is not supported with WebAssembly threads.");
+    }
     const argsRoot = mono_wasm_new_external_root<MonoArray>(args),
         nameRoot = mono_wasm_new_external_root<MonoString>(method_name),
         resultRoot = mono_wasm_new_external_root<MonoObject>(result_address);
@@ -282,6 +286,9 @@ export function mono_wasm_get_global_object_ref(global_name: MonoStringRef, is_e
 // eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export function mono_wasm_invoke_js_blazor(exceptionMessage: Int32Ptr, callInfo: any, arg0: any, arg1: any, arg2: any): void | number {
     try {
+        if (MonoWasmThreads) {
+            throw new Error("Legacy interop is not supported with WebAssembly threads.");
+        }
         const blazorExports = (<any>globalThis).Blazor;
         if (!blazorExports) {
             throw new Error("The blazor.webassembly.js library is not loaded.");