diff --git a/websocket-sharp/Net/WebHeaderCollection.cs b/websocket-sharp/Net/WebHeaderCollection.cs
index cf78c44b..4b9cc2d6 100644
--- a/websocket-sharp/Net/WebHeaderCollection.cs
+++ b/websocket-sharp/Net/WebHeaderCollection.cs
@@ -902,27 +902,6 @@ namespace WebSocketSharp.Net
       return value;
     }
 
-    private void doWithCheckingState (
-      Action <string, string> action, string name, string value, bool setState
-    )
-    {
-      var headerType = getHeaderType (name);
-
-      if (headerType == HttpHeaderType.Response) {
-        doWithCheckingState (action, name, value, true, setState);
-
-        return;
-      }
-
-      if (headerType == HttpHeaderType.Request) {
-        doWithCheckingState (action, name, value, false, setState);
-
-        return;
-      }
-
-      action (name, value);
-    }
-
     private void doWithCheckingState (
       Action <string, string> action,
       string name,