diff --git a/lib/OpenLayers/Map.js b/lib/OpenLayers/Map.js
index da3238ae27..2b824ef1b2 100644
--- a/lib/OpenLayers/Map.js
+++ b/lib/OpenLayers/Map.js
@@ -628,12 +628,12 @@ OpenLayers.Map.prototype = {
                                        this.div.clientHeight);
 
         // Workaround for the fact that hidden elements return 0 for size.
-        if (size.w == 0 && size.h == 0) {
+        if (size.w == 0 && size.h == 0 || isNaN(size.w) && isNaN(size.h)) {
             var dim = OpenLayers.Element.getDimensions(this.div);
             size.w = dim.width;
             size.h = dim.height;
         }
-        if (size.w == 0 && size.h == 0) {
+        if (size.w == 0 && size.h == 0 || isNaN(size.w) && isNaN(size.h)) {
             size.w = parseInt(this.div.style.width);
             size.h = parseInt(this.div.style.height);
         }