diff --git a/lib/OpenLayers/Popup.js b/lib/OpenLayers/Popup.js
index 1491109c56..2fcfaf2c0d 100644
--- a/lib/OpenLayers/Popup.js
+++ b/lib/OpenLayers/Popup.js
@@ -167,8 +167,8 @@ OpenLayers.Popup.prototype = {
         }
         
         if (this.div != null) {
-            this.div.style.width = this.size.w;
-            this.div.style.height = this.size.h;
+            this.div.style.width = this.size.w + "px";
+            this.div.style.height = this.size.h + "px";
         }
     },