diff --git a/core/lib/Drupal/Core/Render/Element/FormElement.php b/core/lib/Drupal/Core/Render/Element/FormElement.php
index ab13289aa7c..173a55cb93f 100644
--- a/core/lib/Drupal/Core/Render/Element/FormElement.php
+++ b/core/lib/Drupal/Core/Render/Element/FormElement.php
@@ -128,10 +128,10 @@ abstract class FormElement extends RenderElement implements FormElementInterface
       $metadata = BubbleableMetadata::createFromRenderArray($element);
       if ($access->isAllowed()) {
         $element['#attributes']['class'][] = 'form-autocomplete';
-        $element['#attached']['library'][] = 'core/drupal.autocomplete';
+        $metadata->addAttachments(['library' => ['core/drupal.autocomplete']]);
         // Provide a data attribute for the JavaScript behavior to bind to.
         $element['#attributes']['data-autocomplete-path'] = $url->getGeneratedUrl();
-        $metadata->merge($url);
+        $metadata = $metadata->merge($url);
       }
       $metadata
         ->merge(BubbleableMetadata::createFromObject($access))
diff --git a/core/modules/system/src/Tests/Form/ElementTest.php b/core/modules/system/src/Tests/Form/ElementTest.php
index d7085dd621e..6555a4f063f 100644
--- a/core/modules/system/src/Tests/Form/ElementTest.php
+++ b/core/modules/system/src/Tests/Form/ElementTest.php
@@ -151,6 +151,9 @@ class ElementTest extends WebTestBase {
     $this->drupalLogin($user);
     $this->drupalGet('form-test/autocomplete');
 
+    // Make sure that the autocomplete library is added.
+    $this->assertRaw('core/misc/autocomplete.js');
+
     $result = $this->xpath('//input[@id="edit-autocomplete-1" and contains(@data-autocomplete-path, "form-test/autocomplete-1")]');
     $this->assertEqual(count($result), 1, 'Ensure that the user does have access to the autocompletion');
     $result = $this->xpath('//input[@id="edit-autocomplete-2" and contains(@data-autocomplete-path, "form-test/autocomplete-2/value")]');