diff --git a/websocket-sharp/Net/HttpUtility.cs b/websocket-sharp/Net/HttpUtility.cs
index 68273fc0..61654737 100644
--- a/websocket-sharp/Net/HttpUtility.cs
+++ b/websocket-sharp/Net/HttpUtility.cs
@@ -134,27 +134,6 @@ namespace WebSocketSharp.Net
                  : -1;
     }
 
-    private static string htmlAttributeEncode (string s)
-    {
-      var buff = new StringBuilder ();
-
-      foreach (var c in s) {
-        buff.Append (
-          c == '"'
-          ? """
-          : c == '&'
-            ? "&"
-            : c == '<'
-              ? "&lt;"
-              : c == '>'
-                ? "&gt;"
-                : c.ToString ()
-        );
-      }
-
-      return buff.ToString ();
-    }
-
     private static string htmlEncode (string s)
     {
       var buff = new StringBuilder ();