--- a/js/src/xpconnect/loader/XPCOMUtils.jsm
+++ b/js/src/xpconnect/loader/XPCOMUtils.jsm
@@ -107,17 +107,17 @@ const Cr = Components.results;
 var XPCOMUtils = {
   /**
    * Generate a QueryInterface implementation. The returned function must be
    * assigned to the 'QueryInterface' property of a JS object. When invoked on
    * that object, it checks if the given iid is listed in the |interfaces|
    * param, and if it is, returns |this| (the object it was called on).
    */
   generateQI: function(interfaces) {
-    return makeQI([i.name for each(i in interfaces)]);
+    return makeQI([i.name for each (i in interfaces) if (i)]);
   },
 
   /**
    * Generate the NSGetModule function (along with the module definition).
    * See the parameters to generateModule.
    */
   generateNSGetModule: function(componentsArray, postRegister, preUnregister) {
     return function NSGetModule(compMgr, fileSpec) {