diff --git a/websocket-sharp/Net/HttpUtility.cs b/websocket-sharp/Net/HttpUtility.cs
index baa046d1..732e8a6b 100644
--- a/websocket-sharp/Net/HttpUtility.cs
+++ b/websocket-sharp/Net/HttpUtility.cs
@@ -405,6 +405,11 @@ namespace WebSocketSharp.Net
              || (c >= 'a' && c <= 'z');
     }
 
+    private static bool isNumeric (byte b)
+    {
+      return b >= 48 && b <= 57;
+    }
+
     private static bool isNumeric (char c)
     {
       return c >= '0' && c <= '9';