diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 25f75c7..f08c9d7 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -713,6 +713,7 @@ function system_schema() {
     'primary key' => array('collection', 'name'),
     'indexes' => array(
       'all' => array('name', 'collection', 'expire'),
+      'expire' => array('expire'),
     ),
   );