diff --git a/lib/OpenLayers/Layer/Grid.js b/lib/OpenLayers/Layer/Grid.js
index 2221362be9..b4c91d40ef 100644
--- a/lib/OpenLayers/Layer/Grid.js
+++ b/lib/OpenLayers/Layer/Grid.js
@@ -44,6 +44,8 @@ OpenLayers.Layer.Grid.prototype =
     destroy: function() {
         this.clearGrid();
         this.grid = null;
+        this.alpha = null;
+        this.tileSize = null;
         OpenLayers.Layer.HTTPRequest.prototype.destroy.apply(this, arguments); 
     },