diff --git a/lib/OpenLayers/Layer/Grid.js b/lib/OpenLayers/Layer/Grid.js
index 6a916ff348..be2ea695f7 100644
--- a/lib/OpenLayers/Layer/Grid.js
+++ b/lib/OpenLayers/Layer/Grid.js
@@ -701,7 +701,7 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
         var tlLayer = this.grid[0][0].position;
         var offsetX = parseInt(this.map.layerContainerDiv.style.left);
         var offsetY = parseInt(this.map.layerContainerDiv.style.top);
-        tlViewPort = tlLayer.add(offsetX, offsetY);
+        var tlViewPort = tlLayer.add(offsetX, offsetY);
         if (tlViewPort.x > -this.tileSize.w * (buffer - 1)) {
             this.shiftColumn(true);
         } else if (tlViewPort.x < -this.tileSize.w * buffer) {