diff --git a/mozilla/toolkit/mozapps/update/content/updates.js b/mozilla/toolkit/mozapps/update/content/updates.js
index 3d31c16ae67..9694cc9f4ed 100755
--- a/mozilla/toolkit/mozapps/update/content/updates.js
+++ b/mozilla/toolkit/mozapps/update/content/updates.js
@@ -322,7 +322,8 @@ var gUpdates = {
    */
   setUpdate: function(update) {
     this.update = update;
-    this.update.QueryInterface(Components.interfaces.nsIWritablePropertyBag);
+    if (this.update)
+      this.update.QueryInterface(Components.interfaces.nsIWritablePropertyBag);
   },
   
   /**