diff --git a/lib/OpenLayers/Layer/Grid.js b/lib/OpenLayers/Layer/Grid.js
index d2565aca0c..a0e064a8bf 100644
--- a/lib/OpenLayers/Layer/Grid.js
+++ b/lib/OpenLayers/Layer/Grid.js
@@ -267,8 +267,8 @@ OpenLayers.Layer.Grid.prototype =
             // if the test grid coordinates are within the bounds of the 
             //  grid, get a reference to the tile.
             var tile = null;
-            if ((testRow < this.grid.length) && 
-                (testCell < this.grid[0].length)) {
+            if ((testRow < this.grid.length) && (testRow >= 0) &&
+                (testCell < this.grid[0].length) && (testCell >= 0)) {
                 tile = this.grid[testRow][testCell];
             }