diff --git a/lib/OpenLayers/Layer/Grid.js b/lib/OpenLayers/Layer/Grid.js
index 42b850bc63..61b9fbb330 100644
--- a/lib/OpenLayers/Layer/Grid.js
+++ b/lib/OpenLayers/Layer/Grid.js
@@ -979,9 +979,10 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
         var offsetX = parseInt(this.map.layerContainerDiv.style.left);
         var offsetY = parseInt(this.map.layerContainerDiv.style.top);
         var tlViewPort = tlLayer.add(offsetX, offsetY);
-        var tileSize = this.tileSize.clone();
-        tileSize.w *= scale;
-        tileSize.h *= scale;
+        var tileSize = {
+            w: this.tileSize.w * scale,
+            h: this.tileSize.h * scale
+        };
         if (tlViewPort.x > -tileSize.w * (buffer - 1)) {
             this.shiftColumn(true);
         } else if (tlViewPort.x < -tileSize.w * buffer) {