diff --git a/lib/OpenLayers/Layer/Grid.js b/lib/OpenLayers/Layer/Grid.js
index d77aaa643f..ba6af27c49 100644
--- a/lib/OpenLayers/Layer/Grid.js
+++ b/lib/OpenLayers/Layer/Grid.js
@@ -276,6 +276,13 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
      * startrow
      */
     gridLayout: null,
+    
+    /**
+     * Property: rowSign
+     * {Number} 1 for grids starting at the top, -1 for grids starting at the
+     * bottom. This is used for several grid index and offset calculations.
+     */
+    rowSign: null,
 
     /**
      * Constructor: OpenLayers.Layer.Grid
@@ -308,6 +315,8 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
                 this.moveTimerId = null;
             }, this);
         }
+        
+        this.rowSign = this.tileOriginCorner.substr(0, 1) === "t" ? 1 : -1;
     },
 
     /**
@@ -884,7 +893,7 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
         var offsetlon = bounds.left - origin.lon;
         var tilecol = Math.floor(offsetlon/tilelon) - this.buffer;
         
-        var rowSign = this.tileOriginCorner.substr(0, 1) === "t" ? 1 : -1;
+        var rowSign = this.rowSign;
 
         var offsetlat = rowSign * (origin.lat - bounds.top + tilelat);  
         var tilerow = Math[~rowSign ? 'floor' : 'ceil'](offsetlat/tilelat) - this.buffer * rowSign;
@@ -939,7 +948,7 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
         var tilelat = tileLayout.tilelat;
         var startcol = tileLayout.startcol;
         var startrow = tileLayout.startrow;
-        var rowSign = this.tileOriginCorner.substr(0, 1) === "t" ? 1 : -1;
+        var rowSign = this.rowSign;
         return new OpenLayers.Bounds(
             origin.lon + (startcol + col) * tilelon,
             origin.lat - (startrow + row * rowSign) * tilelat * rowSign,
@@ -1207,7 +1216,7 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
         var grid = this.grid;
         var rowIndex = prepend ? 0 : (grid.length - 1);
         var sign = prepend ? -1 : 1;
-        var rowSign = this.tileOriginCorner.substr(0, 1) === "t" ? 1 : -1;
+        var rowSign = this.rowSign;
         var tileLayout = this.gridLayout;
         tileLayout.startrow += sign * rowSign;