diff --git a/lib/OpenLayers/Control/OverviewMap.js b/lib/OpenLayers/Control/OverviewMap.js
index 1847340b94..7712a46566 100644
--- a/lib/OpenLayers/Control/OverviewMap.js
+++ b/lib/OpenLayers/Control/OverviewMap.js
@@ -111,7 +111,7 @@ OpenLayers.Control.OverviewMap.prototype =
         this.extentRectangle.style.overflow = 'hidden';
         this.extentRectangle.style.backgroundImage = 'url(' +
                                         OpenLayers.Util.getImagesLocation() +
-                                        '/blank.png)';
+                                        'blank.gif)';
         this.extentRectangle.className = this.displayClass+'ExtentRectangle';
         this.mapDiv.appendChild(this.extentRectangle);