diff --git a/websocket-sharp/Net/HttpListener.cs b/websocket-sharp/Net/HttpListener.cs
index ce6cf15e..8fb69999 100644
--- a/websocket-sharp/Net/HttpListener.cs
+++ b/websocket-sharp/Net/HttpListener.cs
@@ -379,7 +379,9 @@ namespace WebSocketSharp.Net
     /// </exception>
     public string Realm {
       get {
-        CheckDisposed ();
+        if (_disposed)
+          throw new ObjectDisposedException (_objectName);
+
         return _realm;
       }