diff --git a/websocket-sharp/Ext.cs b/websocket-sharp/Ext.cs
index 1f32ef8f..9eadcefd 100644
--- a/websocket-sharp/Ext.cs
+++ b/websocket-sharp/Ext.cs
@@ -1473,50 +1473,6 @@ namespace WebSocketSharp
       return false;
     }
 
-    /// <summary>
-    /// Determines whether the specified HTTP request is an upgrade request to
-    /// switch to the specified protocol.
-    /// </summary>
-    /// <returns>
-    /// <c>true</c> if <paramref name="request"/> is an upgrade request to
-    /// switch to <paramref name="protocol"/>; otherwise, <c>false</c>.
-    /// </returns>
-    /// <param name="request">
-    /// A <see cref="HttpListenerRequest"/> to test.
-    /// </param>
-    /// <param name="protocol">
-    /// A <see cref="string"/> that specifies the name of the protocol.
-    /// </param>
-    /// <exception cref="ArgumentNullException">
-    ///   <para>
-    ///   <paramref name="request"/> is <see langword="null"/>.
-    ///   </para>
-    ///   <para>
-    ///   -or-
-    ///   </para>
-    ///   <para>
-    ///   <paramref name="protocol"/> is <see langword="null"/>.
-    ///   </para>
-    /// </exception>
-    /// <exception cref="ArgumentException">
-    /// <paramref name="protocol"/> is an empty string.
-    /// </exception>
-    public static bool IsUpgradeRequest (
-      this HttpListenerRequest request, string protocol
-    )
-    {
-      if (request == null)
-        throw new ArgumentNullException ("request");
-
-      if (protocol == null)
-        throw new ArgumentNullException ("protocol");
-
-      if (protocol.Length == 0)
-        throw new ArgumentException ("An empty string.", "protocol");
-
-      return request.Headers.Upgrades (protocol);
-    }
-
     /// <summary>
     /// Determines whether the specified string is a URI string.
     /// </summary>
diff --git a/websocket-sharp/Net/HttpListenerRequest.cs b/websocket-sharp/Net/HttpListenerRequest.cs
index fe72aa88..34d9aa8a 100644
--- a/websocket-sharp/Net/HttpListenerRequest.cs
+++ b/websocket-sharp/Net/HttpListenerRequest.cs
@@ -610,6 +610,11 @@ namespace WebSocketSharp.Net
       }
     }
 
+    internal bool IsUpgradeRequest (string protocol)
+    {
+      return _headers.Upgrades (protocol);
+    }
+
     internal void SetRequestLine (string requestLine)
     {
       var parts = requestLine.Split (new[] { ' ' }, 3);