diff --git a/lib/OpenLayers/Control/ZoomBox.js b/lib/OpenLayers/Control/ZoomBox.js
index 202f474fd6..c83ed80b3b 100644
--- a/lib/OpenLayers/Control/ZoomBox.js
+++ b/lib/OpenLayers/Control/ZoomBox.js
@@ -54,7 +54,7 @@ OpenLayers.Control.ZoomBox = OpenLayers.Class(OpenLayers.Control, {
                 var pixHeight = Math.abs(position.top-position.bottom);
                 var zoomFactor = Math.min((this.map.size.h / pixHeight),
                     (this.map.size.w / pixWidth));
-                var extent = map.getExtent();
+                var extent = this.map.getExtent();
                 var center = this.map.getLonLatFromPixel(
                     position.getCenterPixel());
                 var xmin = center.lon - (extent.getWidth()/2)*zoomFactor;