diff --git a/websocket-sharp/Net/WebHeaderCollection.cs b/websocket-sharp/Net/WebHeaderCollection.cs
index 4b9cc2d6..bd472e6c 100644
--- a/websocket-sharp/Net/WebHeaderCollection.cs
+++ b/websocket-sharp/Net/WebHeaderCollection.cs
@@ -902,25 +902,6 @@ namespace WebSocketSharp.Net
       return value;
     }
 
-    private void doWithCheckingState (
-      Action <string, string> action,
-      string name,
-      string value,
-      bool response,
-      bool setState
-    )
-    {
-      checkState (response);
-      action (name, value);
-
-      setState = setState && _state == HttpHeaderType.Unspecified;
-
-      if (!setState)
-        return;
-
-      _state = response ? HttpHeaderType.Response : HttpHeaderType.Request;
-    }
-
     private void doWithoutCheckingName (
       Action <string, string> action, string name, string value
     )