diff --git a/websocket-sharp/Net/HttpListenerRequest.cs b/websocket-sharp/Net/HttpListenerRequest.cs
index 2ee9382f..6f24f5d9 100644
--- a/websocket-sharp/Net/HttpListenerRequest.cs
+++ b/websocket-sharp/Net/HttpListenerRequest.cs
@@ -829,6 +829,7 @@ namespace WebSocketSharp.Net
 
       if (!method.IsHttpMethod (ver)) {
         _context.ErrorMessage = "Invalid request line (method)";
+        _context.ErrorStatusCode = 501;
 
         return;
       }