diff --git a/web/grab_to_pan.js b/web/grab_to_pan.js
index f27f74f6e..c6cb38c8c 100644
--- a/web/grab_to_pan.js
+++ b/web/grab_to_pan.js
@@ -1,4 +1,4 @@
-/* Copyright 2013 Rob Wu <gwnRob@gmail.com>
+/* Copyright 2013 Rob Wu <rob@robwu.nl>
  * https://github.com/Rob--W/grab-to-pan.js
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -215,7 +215,7 @@
       // http://www.w3.org/TR/DOM-Level-3-Events/#events-MouseEvent-buttons
       // Firefox 15+
       // Internet Explorer 10+
-      return !(event.buttons | 1);
+      return !(event.buttons & 1);
     }
     if (isChrome15OrOpera15plus || isSafari6plus) {
       // Chrome 14+