diff --git a/lib/GeoExt/widgets/ZoomSlider.js b/lib/GeoExt/widgets/ZoomSlider.js
index 55d5b607..fc7d791b 100644
--- a/lib/GeoExt/widgets/ZoomSlider.js
+++ b/lib/GeoExt/widgets/ZoomSlider.js
@@ -217,7 +217,7 @@ GeoExt.ZoomSlider = Ext.extend(Ext.slider.SingleSlider, {
                 this.minValue = Math.max(minZoom, layer.minZoomLevel || 0);
             }
             if(this.initialConfig.maxValue === undefined) {
-                this.maxValue = layer.minZoomLevel == null ?
+                this.maxValue = layer.maxZoomLevel == null ?
                     layer.numZoomLevels - 1 : layer.maxZoomLevel;
             }
             // reset the thumb value so it gets repositioned when we call update