diff --git a/src/Transports.AspNetCore/WebSockets/BaseSubscriptionServer.Observer.cs b/src/Transports.AspNetCore/WebSockets/BaseSubscriptionServer.Observer.cs
index 2d3b7ab1..195368df 100644
--- a/src/Transports.AspNetCore/WebSockets/BaseSubscriptionServer.Observer.cs
+++ b/src/Transports.AspNetCore/WebSockets/BaseSubscriptionServer.Observer.cs
@@ -73,6 +73,8 @@ public async void OnNext(ExecutionResult value)
                 await _server.SendDataAsync(_id, value);
                 if (_closeAfterAnyError && value.Errors?.Count > 0)
                 {
+                    if (Interlocked.Exchange(ref _done, 1) == 1)
+                        return;
                     await _server.SendCompletedAsync(_id);
                 }
             }