diff --git a/core/lib/Drupal/Core/Updater/Theme.php b/core/lib/Drupal/Core/Updater/Theme.php
index 72328c0..8647e2a 100644
--- a/core/lib/Drupal/Core/Updater/Theme.php
+++ b/core/lib/Drupal/Core/Updater/Theme.php
@@ -103,7 +103,7 @@ public function postInstallTasks() {
       $link_options = array(
         'attributes' => array(
           'class' => array(
-          'button',
+            'button',
           ),
         ),
       );