diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index 042718b..e3a3122 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -803,7 +803,7 @@ public function prepareForm($form_id, &$form, FormStateInterface &$form_state) {
       $form['#attributes']['data-drupal-selector'] = Html::getId($form_id);
     }
 
-    $form = NestedArray::mergeDeep($this->elementInfo->getInfo('form'), $form);
+    $form = NestedArray::mergeDeepArray([$this->elementInfo->getInfo('form'), $form], TRUE);
     $form += ['#tree' => FALSE, '#parents' => []];
     $form['#validate'][] = '::validateForm';
     $form['#submit'][] = '::submitForm';
@@ -908,7 +908,7 @@ public function doBuildForm($form_id, &$element, FormStateInterface &$form_state
     // Use element defaults.
     if (isset($element['#type']) && empty($element['#defaults_loaded']) && ($info = $this->elementInfo->getInfo($element['#type']))) {
       // Overlay $info onto $element, retaining preexisting keys in $element.
-      $element = NestedArray::mergeDeep($info, $element);
+      $element = NestedArray::mergeDeepArray([$info, $element], TRUE);
       $element['#defaults_loaded'] = TRUE;
     }
     // Assign basic defaults common for all form elements.
@@ -1011,7 +1011,7 @@ public function doBuildForm($form_id, &$element, FormStateInterface &$form_state
       // Prior to checking properties of child elements, their default
       // properties need to be loaded.
       if (isset($element[$key]['#type']) && empty($element[$key]['#defaults_loaded']) && ($info = $this->elementInfo->getInfo($element[$key]['#type']))) {
-        $element[$key] = NestedArray::mergeDeep($info, $element[$key]);
+        $element[$key] = NestedArray::mergeDeepArray([$info, $element[$key]], TRUE);
         $element[$key]['#defaults_loaded'] = TRUE;
       }