diff --git a/dotnet/src/Microsoft.AutoGen/Agents/Services/Grpc/GrpcGateway.cs b/dotnet/src/Microsoft.AutoGen/Agents/Services/Grpc/GrpcGateway.cs
index cb9a00be7492..0bd35b2b25cd 100644
--- a/dotnet/src/Microsoft.AutoGen/Agents/Services/Grpc/GrpcGateway.cs
+++ b/dotnet/src/Microsoft.AutoGen/Agents/Services/Grpc/GrpcGateway.cs
@@ -110,9 +110,15 @@ internal async Task OnReceivedMessageAsync(GrpcWorkerConnection connection, Mess
                 await AddSubscriptionAsync(connection, message.AddSubscriptionRequest);
                 break;
             default:
-                throw new InvalidOperationException($"Unknown message type for message '{message}'.");
+                // if it wasn't recognized return bad request
+                await RespondBadRequestAsync(connection, message.RequestId, $"Unknown message type for message '{message}'.");
+                break;
         };
     }
+    private async ValueTask RespondBadRequestAsync(GrpcWorkerConnection connection, string requestId, string error)
+    {
+        throw new RpcException(new Status(StatusCode.InvalidArgument, error));
+    }
     private async ValueTask AddSubscriptionAsync(GrpcWorkerConnection connection, AddSubscriptionRequest request)
     {
         var topic = request.Subscription.TypeSubscription.TopicType;