diff --git a/websocket-sharp/Net/WebHeaderCollection.cs b/websocket-sharp/Net/WebHeaderCollection.cs
index f525e2e9..976a1bd9 100644
--- a/websocket-sharp/Net/WebHeaderCollection.cs
+++ b/websocket-sharp/Net/WebHeaderCollection.cs
@@ -1247,7 +1247,7 @@ namespace WebSocketSharp.Net
     /// </exception>
     public void Add (HttpRequestHeader header, string value)
     {
-      value = checkValue (value);
+      value = checkValue (value, "value");
 
       var key = header.ToString ();
       var name = getHeaderName (key);