diff --git a/websocket-sharp/Server/WebSocketServer.cs b/websocket-sharp/Server/WebSocketServer.cs
index 1ea37f25..0bd2f595 100644
--- a/websocket-sharp/Server/WebSocketServer.cs
+++ b/websocket-sharp/Server/WebSocketServer.cs
@@ -859,7 +859,7 @@ namespace WebSocketSharp.Server
         }
       }
 
-      if (_state == ServerState.Start)
+      if (_state == ServerState.Ready || _state == ServerState.Start)
         abort ();
     }