@ -138,8 +138,10 @@ namespace WebSocketSharp.Net
/// </exception>
public void Add (string uriPrefix)
{
if (_listener.IsDisposed)
throw new ObjectDisposedException (_listener.GetType ().ToString ());
HttpListenerPrefix.CheckPrefix (uriPrefix);
_listener.CheckDisposed ();
if (_prefixes.Contains (uriPrefix))
return;