diff --git a/websocket-sharp/Net/WebSockets/TcpListenerWebSocketContext.cs b/websocket-sharp/Net/WebSockets/TcpListenerWebSocketContext.cs
index 762c762f..81b6a29a 100644
--- a/websocket-sharp/Net/WebSockets/TcpListenerWebSocketContext.cs
+++ b/websocket-sharp/Net/WebSockets/TcpListenerWebSocketContext.cs
@@ -39,7 +39,6 @@ using System.Collections.Specialized;
 using System.IO;
 using System.Net.Security;
 using System.Net.Sockets;
-using System.Security.Cryptography.X509Certificates;
 using System.Security.Principal;
 using System.Text;