diff --git a/src/input/Mouse.js b/src/input/Mouse.js
index 0a429375..033236f0 100644
--- a/src/input/Mouse.js
+++ b/src/input/Mouse.js
@@ -165,7 +165,7 @@ Phaser.Mouse.prototype = {
             event.preventDefault();
         }
 
-        this.button = event.which;
+        this.button = event.button;
 
         if (this.mouseDownCallback)
         {