diff --git a/modules/system/system.install b/modules/system/system.install
index ba6a4a3..2fa642e 100644
--- a/modules/system/system.install
+++ b/modules/system/system.install
@@ -3090,10 +3090,15 @@ function system_update_7077() {
 }

 /**
- * Set the {sessions}.uid field default value to 0, making possible a schema
- * change for the {sessions} table for future Drupal 8 migration.
+ * Change the {sessions}.uid default value to 0.
  */
-function system_update_7074() {
+function system_update_7078() {
+  global $user;
+  if ($user->uid) {
+    db_delete('sessions')
+      ->condition('uid', $user->uid, '<>')
+      ->execute();
+  }
   db_change_field('sessions', 'uid', 'uid', array(
     'description' => 'The {users}.uid corresponding to a session, or 0 for anonymous user.',
     'type' => 'int',