diff --git a/lib/OpenLayers/Layer/Grid.js b/lib/OpenLayers/Layer/Grid.js
index ec67a6305f..a7db5bfa13 100644
--- a/lib/OpenLayers/Layer/Grid.js
+++ b/lib/OpenLayers/Layer/Grid.js
@@ -204,7 +204,7 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
      */
     setTileSize: function(size) { 
         if (this.singleTile) {
-            var size = this.map.getSize().clone();
+            size = this.map.getSize().clone();
             size.h = parseInt(size.h * this.ratio);
             size.w = parseInt(size.w * this.ratio);
         }