diff --git a/websocket-sharp/Net/HttpListener.cs b/websocket-sharp/Net/HttpListener.cs
index ca8d3b21..c40fa376 100644
--- a/websocket-sharp/Net/HttpListener.cs
+++ b/websocket-sharp/Net/HttpListener.cs
@@ -474,7 +474,9 @@ namespace WebSocketSharp.Net
       }
 
       set {
-        CheckDisposed ();
+        if (_disposed)
+          throw new ObjectDisposedException (_objectName);
+
         _userCredFinder = value;
       }
     }