diff --git a/lib/Drupal/Core/Render/Element/MachineName.php b/lib/Drupal/Core/Render/Element/MachineName.php
index 66c85c7..dd37f3f 100644
--- a/lib/Drupal/Core/Render/Element/MachineName.php
+++ b/lib/Drupal/Core/Render/Element/MachineName.php
@@ -191,6 +191,10 @@ class MachineName extends Textfield {
 
     $element['#attached']['library'][] = 'core/drupal.machine-name';
     $element['#attached']['drupalSettings']['machineName']['#' . $source['#id']] = $element['#machine_name'];
+    $settings = &$element['#attached']['drupalSettings']['machineName']['#' . $source['#id']];
+    if (isset($settings['exists']) && is_array($settings['exists']) && is_object($settings['exists'][0])) {
+      $settings['exists'][0] = get_class($settings['exists'][0]);
+    }
     $element['#attached']['drupalSettings']['langcode'] = $language->getId();
 
     return $element;