diff --git a/core/modules/image/image.field.inc b/core/modules/image/image.field.inc
index 245d149..015bb26 100644
--- a/core/modules/image/image.field.inc
+++ b/core/modules/image/image.field.inc
@@ -7,6 +7,7 @@
 
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Template\Attribute;
 
 /**
  * Prepares variables for image widget templates.
@@ -20,8 +21,7 @@
 function template_preprocess_image_widget(&$variables) {
   $element = $variables['element'];
 
-  $variables['attributes'] = $element['#attributes'];
-  $variables['attributes']['class'] = array('image-widget', 'form-managed-file', 'clearfix');
+  $variables['attributes'] = new Attribute(array('class' => array('image-widget', 'form-managed-file', 'clearfix')));
 
   if (!empty($element['fids']['#value'])) {
     $file = reset($element['#files']);