Index: modules/system/system.install
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.install,v
retrieving revision 1.522
diff -u -p -r1.522 system.install
--- modules/system/system.install	5 Nov 2010 19:05:02 -0000	1.522
+++ modules/system/system.install	10 Nov 2010 23:59:43 -0000
@@ -2910,7 +2910,9 @@ function system_update_7065() {
     'length' => 128,
     'not null' => TRUE,
   );
-  db_change_field('sessions', 'sid', 'sid', $spec);
+  db_drop_primary_key('sessions');
+  db_change_field('sessions', 'sid', 'sid', $spec,
+    array('primary key' => array('sid', 'ssid')));
 }
 
 /**