diff --git a/websocket-sharp/Net/HttpListenerResponse.cs b/websocket-sharp/Net/HttpListenerResponse.cs
index b2561389..9bae3dc0 100644
--- a/websocket-sharp/Net/HttpListenerResponse.cs
+++ b/websocket-sharp/Net/HttpListenerResponse.cs
@@ -962,7 +962,7 @@ namespace WebSocketSharp.Net
         throw new ArgumentNullException ("cookie");
 
       if (!canAddOrUpdate (cookie)) {
-        var msg = "It cannot be replaced.";
+        var msg = "It cannot be updated.";
         throw new ArgumentException (msg, "cookie");
       }