diff --git a/websocket-sharp/WebSocket.cs b/websocket-sharp/WebSocket.cs
index ca34b8b4..4e59ae64 100644
--- a/websocket-sharp/WebSocket.cs
+++ b/websocket-sharp/WebSocket.cs
@@ -672,6 +672,11 @@ namespace WebSocketSharp
         throw new WebSocketException (CloseStatusCode.ProtocolError, msg);
       }
 
+      if (!customCheckIfValidHandshakeRequest (_context, out msg)) {
+        sendHttpResponse (createHandshakeCloseResponse (HttpStatusCode.BadRequest));
+        throw new WebSocketException (CloseStatusCode.PolicyViolation, msg);
+      }
+
       if (_protocol != null
           && !_context.SecWebSocketProtocols.Contains (protocol => protocol == _protocol)
       ) {
@@ -723,10 +728,6 @@ namespace WebSocketSharp
         return false;
       }
 
-      message = CustomHandshakeRequestChecker (context);
-      if (message != null)
-        return false;
-
       return true;
     }
 
@@ -984,6 +985,14 @@ namespace WebSocketSharp
       return ret;
     }
 
+    // As server
+    private bool customCheckIfValidHandshakeRequest (WebSocketContext context, out string message)
+    {
+      message = null;
+      return _handshakeRequestChecker == null
+             || (message = _handshakeRequestChecker (context)) == null;
+    }
+
     private MessageEventArgs dequeueFromMessageEventQueue ()
     {
       lock (_forMessageEventQueue)