diff --git a/core/lib/Drupal/Component/Utility/Html.php b/core/lib/Drupal/Component/Utility/Html.php
index b10f203..659cb27 100644
--- a/core/lib/Drupal/Component/Utility/Html.php
+++ b/core/lib/Drupal/Component/Utility/Html.php
@@ -144,7 +144,7 @@ public static function getUniqueId($id) {
     // will be merged with content already on the base page. The HTML IDs must
     // be unique for the fully merged content. Therefore use unique IDs.
     if (static::$isAjax) {
-      return static::getId($id) . '--' . uniqid();
+      return static::getId($id) . '--' . Crypt::randomBytesBase64(8);
     }
 
     // seenIdsInit is only useful for tests anymore.
diff --git a/core/misc/ajax.js b/core/misc/ajax.js
index 8f2b8cd..76ee918 100644
--- a/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -379,7 +379,7 @@
   /**
    * Request parameter to indicate that a request is a drupal ajax request.
    */
-   DRupal.ajax.AJAX_REQUEST_PARAMETER = '_drupal_ajax';
+   Drupal.ajax.AJAX_REQUEST_PARAMETER = '_drupal_ajax';
 
   /**
    * Execute the ajax request.
diff --git a/core/modules/file/src/Element/ManagedFile.php b/core/modules/file/src/Element/ManagedFile.php
index 40d0c31..740791c 100644
--- a/core/modules/file/src/Element/ManagedFile.php
+++ b/core/modules/file/src/Element/ManagedFile.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\file\Element;
 
+use Drupal\Component\Utility\Html;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\Element\FormElement;
 use Drupal\Core\Url;
@@ -130,9 +131,6 @@ public static function valueCallback(&$element, $input, FormStateInterface $form
    * support for a default value.
    */
   public static function processManagedFile(&$element, FormStateInterface $form_state, &$complete_form) {
-    // Append the '-upload' to the #id so the field label's 'for' attribute
-    // corresponds with the file element.
-    $element['#id'] .= '-upload';
 
     // This is used sometimes so let's implode it just once.
     $parents_prefix = implode('_', $element['#parents']);
@@ -144,6 +142,9 @@ public static function processManagedFile(&$element, FormStateInterface $form_st
     $element['#files'] = !empty($fids) ? File::loadMultiple($fids) : FALSE;
     $element['#tree'] = TRUE;
 
+    // Generate a wrapper html ID. All we need is that its unique.
+    $ajax_wrapper_id = Html::getUniqueId('ajax-wrapper');
+
     $ajax_settings = [
       'url' => Url::fromRoute('file.ajax_upload'),
       'options' => [
@@ -152,7 +153,7 @@ public static function processManagedFile(&$element, FormStateInterface $form_st
           'form_build_id' => $complete_form['form_build_id']['#value'],
         ],
       ],
-      'wrapper' => $element['#id'] . '-ajax-wrapper',
+      'wrapper' => $ajax_wrapper_id,
       'effect' => 'fade',
       'progress' => [
         'type' => $element['#progress_indicator'],
@@ -259,8 +260,12 @@ public static function processManagedFile(&$element, FormStateInterface $form_st
       $element['upload']['#attached']['drupalSettings']['file']['elements']['#' . $element['#id']] = $extension_list;
     }
 
+    // Let #id point of the file element, so the field label's 'for' corresponds
+    // with it.
+    $element['#id'] = &$element['upload']['#id'];
+
     // Prefix and suffix used for Ajax replacement.
-    $element['#prefix'] = '<div id="' . $element['#id'] . '-ajax-wrapper">';
+    $element['#prefix'] = '<div id="' . $ajax_wrapper_id . '">';
     $element['#suffix'] = '</div>';
 
     return $element;