diff --git a/modules/authcache_ajax/authcache_ajax.js b/modules/authcache_ajax/authcache_ajax.js
index 17e0d7b..53ed187 100644
--- a/modules/authcache_ajax/authcache_ajax.js
+++ b/modules/authcache_ajax/authcache_ajax.js
@@ -44,7 +44,8 @@
         $.each(settings.authcacheP13nAjaxFragments, function(frag) {
           var params = this;
           $.each(params, function(url) {
-            var param = this;
+            // In IE<=9 this is an object [object String].
+            var param = this.toString();
             var $targets = $('.authcache-ajax-frag', context).filter(function () {
               // Use attr() instead of data() in order to prevent jQuery from
               // converting numeric strings to integers.