diff --git a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
index f64f20374e..ce5a628af8 100644
--- a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
+++ b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
@@ -291,6 +291,18 @@ private void ProcessRequests(ITestRequestManager testRequestManager)
             catch (Exception ex)
             {
                 EqtTrace.Error("DesignModeClient: Error processing request: {0}", ex);
+
+                // Notify the caller (IDE) about the error so it does not hang
+                // waiting for a response that will never come.
+                try
+                {
+                    _communicationManager.SendMessage(MessageType.ProtocolError, ex.Message);
+                }
+                catch (Exception sendEx)
+                {
+                    EqtTrace.Error("DesignModeClient: Failed to send ProtocolError to client: {0}", sendEx);
+                }
+
                 Stop();
             }
         }
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/EventHandlers/TestRequestHandler.cs b/src/Microsoft.TestPlatform.CrossPlatEngine/EventHandlers/TestRequestHandler.cs
index 0c9fb56ed2..4982e7d9c6 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/EventHandlers/TestRequestHandler.cs
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/EventHandlers/TestRequestHandler.cs
@@ -323,6 +323,32 @@ public bool AttachDebuggerToProcess(AttachDebuggerInfo attachDebuggerInfo)
     }
 
     public void OnMessageReceived(object? sender, MessageReceivedEventArgs messageReceivedArgs)
+    {
+        try
+        {
+            OnMessageReceivedCore(messageReceivedArgs);
+        }
+        catch (Exception ex)
+        {
+            EqtTrace.Error("TestRequestHandler.OnMessageReceived: Failed to process message, sending ProtocolError and closing session: {0}", ex);
+
+            // Notify the caller about the error so it does not hang
+            // waiting for a response that will never come.
+            try
+            {
+                SendData(_dataSerializer.SerializePayload(MessageType.ProtocolError, ex.Message));
+            }
+            catch (Exception sendEx)
+            {
+                EqtTrace.Error("TestRequestHandler.OnMessageReceived: Failed to send ProtocolError: {0}", sendEx);
+            }
+
+            _sessionCompleted.Set();
+            Close();
+        }
+    }
+
+    private void OnMessageReceivedCore(MessageReceivedEventArgs messageReceivedArgs)
     {
         var message = _dataSerializer.DeserializeMessage(messageReceivedArgs.Data!);
         EqtTrace.Info("TestRequestHandler.OnMessageReceived: received message: {0}", message);