diff --git a/lib/OpenLayers/Control/MouseToolbar.js b/lib/OpenLayers/Control/MouseToolbar.js
index 92311835ff..056e56868f 100644
--- a/lib/OpenLayers/Control/MouseToolbar.js
+++ b/lib/OpenLayers/Control/MouseToolbar.js
@@ -170,7 +170,7 @@ OpenLayers.Control.MouseToolbar.prototype =
     switchModeTo: function(mode) {
         if (mode != this.mode) {
             if (this.mode) {
-                this.buttons[this.mode].firstChild.src = this.buttons[this.mode].imgLocation;
+                OpenLayers.Util.modifyAlphaImageDiv(this.buttons[this.mode], null, null, null, this.buttons[this.mode].imgLocation);
             }
             if (this.mode == "measure" && mode != "measure") {
                 for(var i = 0; i < this.measureDivs.length; i++) {
@@ -182,7 +182,7 @@ OpenLayers.Control.MouseToolbar.prototype =
                 this.measureStart = null;
             }
             this.mode = mode;
-            this.buttons[mode].firstChild.src = this.buttons[mode].activeImgLocation;
+            OpenLayers.Util.modifyAlphaImageDiv(this.buttons[mode], null, null, null, this.buttons[mode].activeImgLocation);
         } 
     },