diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Interop/JavaScriptExports.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Interop/JavaScriptExports.cs
index 6bb74c0f42fe8..e2ee42ffec2f6 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Interop/JavaScriptExports.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Interop/JavaScriptExports.cs
@@ -277,7 +277,7 @@ public static void InstallMainSynchronizationContext(JSMarshalerArgument* argume
             }
             catch (Exception ex)
             {
-                arg_exc.ToJS(ex);
+                Environment.FailFast($"InstallMainSynchronizationContext: Unexpected failure (ManagedThreadId {Environment.CurrentManagedThreadId}): " + ex);
             }
         }
 
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSSynchronizationContext.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSSynchronizationContext.cs
index e93b1774d6871..2a2f134e9e9e0 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSSynchronizationContext.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSSynchronizationContext.cs
@@ -294,9 +294,9 @@ private void Pump()
                 // otherwise, we could schedule another round
                 AwaitNewData();
             }
-            catch (Exception e)
+            catch (Exception ex)
             {
-                Environment.FailFast($"JSSynchronizationContext.Pump failed, ManagedThreadId: {Environment.CurrentManagedThreadId}. {Environment.NewLine} {e.StackTrace}");
+                Environment.FailFast($"JSSynchronizationContext.Pump: Unexpected failure (ManagedThreadId {Environment.CurrentManagedThreadId}): " + ex);
             }
         }
 
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/WebWorkerTest.cs b/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/WebWorkerTest.cs
index 24ff04897c2a8..c247ef332921f 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/WebWorkerTest.cs
+++ b/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/WebWorkerTest.cs
@@ -520,6 +520,7 @@ await executor.Execute(async () =>
         }
 
         [Theory, MemberData(nameof(GetTargetThreadsAndBlockingCalls))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99951")]
         public async Task WaitAssertsOnSyncCallback(Executor executor, NamedCall method)
         {
             using var cts = CreateTestCaseTimeoutSource();
@@ -555,6 +556,7 @@ await WebWorkerTestHelper.CallMeBackSync(() =>
         }
 
         [Theory, MemberData(nameof(GetTargetThreadsAndBlockingCalls))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99951")]
         public async Task WaitAssertsOnSyncJSExport(Executor executor, NamedCall method)
         {
             using var cts = CreateTestCaseTimeoutSource();