diff --git a/core/modules/toolbar/toolbar.module b/core/modules/toolbar/toolbar.module
index f3e700c..44e70ff 100644
--- a/core/modules/toolbar/toolbar.module
+++ b/core/modules/toolbar/toolbar.module
@@ -284,16 +284,9 @@ function toolbar_preprocess_html(&$variables) {
     return;
   }
 
-  $attributes = isset($variables['attributes']) ? $variables['attributes'] : array();
-  if (!isset($attributes['class'])) {
-    $attributes['class'] = array();
-  }
-
-  $attributes['class'][] = 'toolbar-tray-open';
-  $attributes['class'][] = 'toolbar-horizontal';
-  $attributes['class'][] = 'toolbar-loading';
-
-  $variables['attributes'] = new Attribute($attributes);
+  $variables['attributes'] = new Attribute(array(
+    'class' => ['toolbar-tray-open', 'toolbar-horizontal', 'toolbar-loading']
+  ));
 }
 
 /**