diff --git a/websocket-sharp/Net/HttpListenerPrefixCollection.cs b/websocket-sharp/Net/HttpListenerPrefixCollection.cs
index 66afe787..dcc54476 100644
--- a/websocket-sharp/Net/HttpListenerPrefixCollection.cs
+++ b/websocket-sharp/Net/HttpListenerPrefixCollection.cs
@@ -194,11 +194,12 @@ namespace WebSocketSharp.Net
     /// </exception>
     public bool Contains (string uriPrefix)
     {
+      if (_listener.IsDisposed)
+        throw new ObjectDisposedException (_listener.GetType ().ToString ());
+
       if (uriPrefix == null)
         throw new ArgumentNullException ("uriPrefix");
 
-      _listener.CheckDisposed ();
-
       return _prefixes.Contains (uriPrefix);
     }