diff --git a/websocket-sharp/Net/WebHeaderCollection.cs b/websocket-sharp/Net/WebHeaderCollection.cs
index 716cd89e..71a5b7b8 100644
--- a/websocket-sharp/Net/WebHeaderCollection.cs
+++ b/websocket-sharp/Net/WebHeaderCollection.cs
@@ -842,7 +842,10 @@ namespace WebSocketSharp.Net
       if (_internallyUsed)
         return;
 
-      if (isRestricted (name, true)) {
+      var headerType = getHeaderType (name);
+      var res = headerType == HttpHeaderType.Response;
+
+      if (isRestricted (name, res)) {
         var msg = "This header must be modified with the appropiate property.";
 
         throw new ArgumentException (msg);