diff --git a/core/lib/Drupal/Core/Render/Element/File.php b/core/lib/Drupal/Core/Render/Element/File.php
index 07bd415..bf2310a 100644
--- a/core/lib/Drupal/Core/Render/Element/File.php
+++ b/core/lib/Drupal/Core/Render/Element/File.php
@@ -44,7 +44,7 @@ public function getInfo() {
    */
   public static function processFile(&$element, FormStateInterface $form_state, &$complete_form) {
     if ($element['#multiple']) {
-      $element['#attributes'] = ['multiple' => 'multiple'];
+      $element['#attributes']['multiple'] = 'multiple';
       $element['#name'] .= '[]';
     }
     return $element;