diff --git a/websocket-sharp/Net/WebHeaderCollection.cs b/websocket-sharp/Net/WebHeaderCollection.cs
index 9201886a..76c5f794 100644
--- a/websocket-sharp/Net/WebHeaderCollection.cs
+++ b/websocket-sharp/Net/WebHeaderCollection.cs
@@ -1814,7 +1814,7 @@ namespace WebSocketSharp.Net
 
       value = checkValue (value);
 
-      checkRestricted (name, true);
+      checkRestricted (name, HttpHeaderType.Response);
       checkAllowed (true);
       set (name, value, HttpHeaderType.Response);
     }