diff --git a/django/contrib/admin/media/js/admin/RelatedObjectLookups.js b/django/contrib/admin/media/js/admin/RelatedObjectLookups.js
index db4ed1a9d17..e5e05a7e325 100644
--- a/django/contrib/admin/media/js/admin/RelatedObjectLookups.js
+++ b/django/contrib/admin/media/js/admin/RelatedObjectLookups.js
@@ -30,7 +30,12 @@ function dismissRelatedLookupPopup(win, chosenId) {
 function showAddAnotherPopup(triggeringLink) {
     var name = triggeringLink.id.replace(/^add_/, '');
     name = name.replace(/\./g, '___');
-    var win = window.open(triggeringLink.href + '?_popup=1', name, 'height=500,width=800,resizable=yes,scrollbars=yes');
+    href = triggeringLink.href
+    if (href.indexOf('?') == -1)
+	href += '?_popup=1';
+    else
+	href += '&_popup=1';
+    var win = window.open(href, name, 'height=500,width=800,resizable=yes,scrollbars=yes');
     win.focus();
     return false;
 }