diff --git a/modules/system/system.install b/modules/system/system.install
index 0b691a20dcea084c80bb3a7ae916ef37b0b5ce5c..c83bc60feb87c544502f77c922f1fd88b0b5f5f1 100644
--- a/modules/system/system.install
+++ b/modules/system/system.install
@@ -1380,7 +1380,10 @@ function system_schema() {
         'not null' => TRUE
       ),
     ),
-    'indexes' => array('value' => array('value')),
+    'indexes' => array(
+      'value' => array('value'),
+      'expire' => array('expire'),
+    ),
     'primary key' => array('name'),
   );