diff --git a/websocket-sharp/Ext.cs b/websocket-sharp/Ext.cs
index 4e041a13..e004217b 100644
--- a/websocket-sharp/Ext.cs
+++ b/websocket-sharp/Ext.cs
@@ -296,6 +296,44 @@ namespace WebSocketSharp
         destination.Write (buff, 0, nread);
     }
 
+    internal static void CopyToAsync (
+      this Stream source,
+      Stream destination,
+      int bufferLength,
+      Action completed,
+      Action<Exception> error)
+    {
+      var buff = new byte[bufferLength];
+
+      AsyncCallback callback = null;
+      callback = ar => {
+        try {
+          var nread = source.EndRead (ar);
+          if (nread <= 0) {
+            if (completed != null)
+              completed ();
+
+            return;
+          }
+
+          destination.Write (buff, 0, nread);
+          source.BeginRead (buff, 0, bufferLength, callback, null);
+        }
+        catch (Exception ex) {
+          if (error != null)
+            error (ex);
+        }
+      };
+
+      try {
+        source.BeginRead (buff, 0, bufferLength, callback, null);
+      }
+      catch (Exception ex) {
+        if (error != null)
+          error (ex);
+      }
+    }
+
     internal static byte[] Decompress (this byte[] data, CompressionMethod method)
     {
       return method == CompressionMethod.Deflate