diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 1272085..6f9dc61 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -2002,6 +2002,18 @@ function system_update_8014() {
 }
 
 /**
+ * Move the system maintenance settings from variable to config.
+ *
+ * @ingroup config_upgrade
+ */
+function system_update_8015() {
+  update_variables_to_config('system.maintenance', array(
+    'maintenance_mode' => 'enabled',
+    'maintenance_mode_message' => 'message',
+  ));
+}
+
+/**
  * @} End of "defgroup updates-7.x-to-8.x".
  * The next series of updates should start at 9000.
  */