diff --git a/lib/OpenLayers/Format/KML.js b/lib/OpenLayers/Format/KML.js
index f76b4ff708..b814eece5a 100644
--- a/lib/OpenLayers/Format/KML.js
+++ b/lib/OpenLayers/Format/KML.js
@@ -1482,7 +1482,7 @@ OpenLayers.Format.KML = OpenLayers.Class(OpenLayers.Format.XML, {
      */
     buildExtendedData: function(attributes) {
         var extendedData = this.createElementNS(this.kmlns, "ExtendedData");
-        for (attributeName in attributes) {
+        for (var attributeName in attributes) {
             // empty, name, description, styleUrl attributes ignored
             if (attributes[attributeName] && attributeName != "name" && attributeName != "description" && attributeName != "styleUrl") {
                 var data = this.createElementNS(this.kmlns, "Data");