diff --git a/websocket-sharp/Net/HttpListenerAsyncResult.cs b/websocket-sharp/Net/HttpListenerAsyncResult.cs
index e72cef68..cf1f520f 100644
--- a/websocket-sharp/Net/HttpListenerAsyncResult.cs
+++ b/websocket-sharp/Net/HttpListenerAsyncResult.cs
@@ -45,7 +45,6 @@
 #endregion
 
 using System;
-using System.Security.Principal;
 using System.Threading;
 
 namespace WebSocketSharp.Net