diff --git a/websocket-sharp/Net/HttpUtility.cs b/websocket-sharp/Net/HttpUtility.cs
index 167da146..83ba1645 100644
--- a/websocket-sharp/Net/HttpUtility.cs
+++ b/websocket-sharp/Net/HttpUtility.cs
@@ -178,6 +178,29 @@ namespace WebSocketSharp.Net
       return buff.ToString ();
     }
 
+    private static string htmlEncode (string s, bool attribute)
+    {
+      var buff = new StringBuilder ();
+
+      foreach (var c in s) {
+        buff.Append (
+          c == '"'
+          ? """
+          : c == '&'
+            ? "&"
+            : c == '<'
+              ? "&lt;"
+              : c == '>'
+                ? "&gt;"
+                : !attribute && c > 159
+                  ? String.Format ("&#{0};", (int) c)
+                  : c.ToString ()
+        );
+      }
+
+      return buff.ToString ();
+    }
+
     private static void initEntities ()
     {
       // Build the dictionary of HTML entity references.