diff --git a/core/core.services.yml b/core/core.services.yml
index e4343f1..b993e6c 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -350,7 +350,7 @@ services:
     tags:
       - { name: event_subscriber }
   entity.autocomplete_matcher:
-    class: Drupal\system\EntityAutocompleteMatcher
+    class: Drupal\Core\Entity\EntityAutocompleteMatcher
     arguments: ['@plugin.manager.entity_reference_selection']
   plugin.manager.entity_reference_selection:
     class: Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginManager
diff --git a/core/lib/Drupal/Core/Render/Element/EntityAutocomplete.php b/core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
similarity index 84%
rename from core/lib/Drupal/Core/Render/Element/EntityAutocomplete.php
rename to core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
index 88e05d9..8a95237 100644
--- a/core/lib/Drupal/Core/Render/Element/EntityAutocomplete.php
+++ b/core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
@@ -2,13 +2,14 @@
 
 /**
  * @file
- * Contains \Drupal\Core\Render\Element\EntityAutocomplete.
+ * Contains \Drupal\Core\Entity\Element\EntityAutocomplete.
  */
 
-namespace Drupal\Core\Render\Element;
+namespace Drupal\Core\Entity\Element;
 
 use Drupal\Component\Utility\Tags;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Render\Element\Textfield;
 use Drupal\user\EntityOwnerInterface;
 
 /**
@@ -30,10 +31,7 @@ public function getInfo() {
     $info['#selection_handler'] = 'default';
     $info['#selection_settings'] = array();
     $info['#tags'] = FALSE;
-    // @todo Use an array for the 'autocreate API' below?
-    $info['#autocreate'] = FALSE;
-    $info['#autocreate_bundle'] = NULL;
-    $info['#autocreate_uid'] = \Drupal::currentUser()->id();
+    $info['#autocreate'] = NULL;
 
     $info['#element_validate'] = array(array($class, 'validateEntityAutocomplete'));
     array_unshift($info['#process'], array($class, 'processEntityAutocomplete'));
@@ -62,11 +60,24 @@ public function getInfo() {
    *
    * @return array
    *   The form element.
+   *
+   * @throws \InvalidArgumentException
+   *   Exception thrown when the #target_type or #autocreate['bundle'] are
+   *   missing.
    */
   public static function processEntityAutocomplete(&$element, FormStateInterface $form_state, &$complete_form) {
     // Nothing to do if there is no target entity type.
     if (empty($element['#target_type'])) {
-      return $element;
+      throw new \InvalidArgumentException('Missing required #target_type parameter.');
+    }
+
+    // Provide default values and sanity checks for the #autocreate parameter.
+    if ($element['#autocreate']) {
+      if (!isset($element['#autocreate']['bundle'])) {
+        throw new \InvalidArgumentException("Missing required #autocreate['bundle'] parameter.");
+      }
+      // Default the autocreate user ID to the current user.
+      $element['#autocreate']['uid'] = $element['#autocreate']['uid'] ?: \Drupal::currentUser()->id();
     }
 
     $element['#autocomplete_route_name'] = 'system.entity_autocomplete';
@@ -114,11 +125,11 @@ public static function validateEntityAutocomplete(&$element, FormStateInterface
             'target_id' => $match,
           );
         }
-        elseif ($autocreate && $element['#autocreate_bundle']) {
+        elseif ($autocreate) {
           // Auto-create item. See
           // \Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem::presave().
           $value[] = array(
-            'entity' => static::createNewEntity($element['#target_type'], $element['#autocreate_bundle'], $input, $element['#autocreate_uid'])
+            'entity' => static::createNewEntity($element['#target_type'], $element['#autocreate']['bundle'], $input, $element['#autocreate']['uid'])
           );
         }
       }
@@ -148,7 +159,7 @@ public static function validateEntityAutocomplete(&$element, FormStateInterface
    *
    * @return \Drupal\Core\Entity\EntityInterface
    */
-  protected static function createNewEntity($entity_type_id, $bundle ,$label, $uid) {
+  protected static function createNewEntity($entity_type_id, $bundle, $label, $uid) {
     $entity_manager = \Drupal::entityManager();
 
     $entity_type = $entity_manager->getDefinition($entity_type_id);
diff --git a/core/modules/system/src/EntityAutocompleteMatcher.php b/core/lib/Drupal/Core/Entity/EntityAutocompleteMatcher.php
similarity index 86%
rename from core/modules/system/src/EntityAutocompleteMatcher.php
rename to core/lib/Drupal/Core/Entity/EntityAutocompleteMatcher.php
index a052209..859f613 100644
--- a/core/modules/system/src/EntityAutocompleteMatcher.php
+++ b/core/lib/Drupal/Core/Entity/EntityAutocompleteMatcher.php
@@ -2,22 +2,22 @@
 
 /**
  * @file
- * Contains \Drupal\system\EntityAutocompleteMatcher.
+ * Contains \Drupal\Core\Entity\EntityAutocompleteMatcher.
  */
 
-namespace Drupal\system;
+namespace Drupal\Core\Entity;
 
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\Tags;
 use Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginManagerInterface;
 
 /**
- * Helper class to get autocompletion results for entity reference.
+ * Matcher class to get autocompletion results for entity reference.
  */
 class EntityAutocompleteMatcher {
 
   /**
-   * The Entity reference selection handler plugin manager.
+   * The entity reference selection handler plugin manager.
    *
    * @var \Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginManagerInterface
    */
@@ -27,7 +27,7 @@ class EntityAutocompleteMatcher {
    * Constructs a EntityAutocompleteMatcher object.
    *
    * @param \Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginManagerInterface $selection_manager
-   *   The Entity reference selection handler plugin manager.
+   *   The entity reference selection handler plugin manager.
    */
   public function __construct(SelectionPluginManagerInterface $selection_manager) {
     $this->selectionHandlerManager = $selection_manager;
@@ -36,9 +36,6 @@ public function __construct(SelectionPluginManagerInterface $selection_manager)
   /**
    * Returns matched labels based on a given search string.
    *
-   * This function can be used by other modules that wish to pass a mocked
-   * definition of the field on instance.
-   *
    * @param string $target_type
    *   The ID of the target entity type.
    * @param string $selection_handler
@@ -52,7 +49,8 @@ public function __construct(SelectionPluginManagerInterface $selection_manager)
    *   Thrown when the current user doesn't have access to the specifies entity.
    *
    * @return array
-   *   A list of matched entity labels.
+   *   An array of matched entity labels, in the format required by the AJAX
+   *   autocomplete API (e.g. array('value' => $value, 'label' => $label)).
    *
    * @see \Drupal\system\Controller\EntityAutocompleteController
    */
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/AutocompleteWidget.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/AutocompleteWidget.php
index 90b81d5..bc646ec 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/AutocompleteWidget.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/AutocompleteWidget.php
@@ -100,15 +100,19 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
       '#target_type' => $this->getFieldSetting('target_type'),
       '#selection_handler' => $this->getFieldSetting('handler'),
       '#selection_settings' => $this->getFieldSetting('handler_settings'),
-      '#autocreate' => $this->getSelectionHandlerSetting('auto_create'),
-      '#autocreate_bundle' => $this->getAutocreateBundle(),
-      '#autocreate_uid' => ($entity instanceof EntityOwnerInterface) ? $entity->getOwnerId() : \Drupal::currentUser()->id(),
       '#maxlength' => 1024,
       '#default_value' => implode(', ', $this->getLabels($items, $delta)),
       '#size' => $this->getSetting('size'),
       '#placeholder' => $this->getSetting('placeholder'),
     );
 
+    if ($this->getSelectionHandlerSetting('auto_create')) {
+      $element['#autocreate'] = array(
+        'bundle' => $this->getAutocreateBundle(),
+        'uid' => ($entity instanceof EntityOwnerInterface) ? $entity->getOwnerId() : \Drupal::currentUser()->id()
+      );
+    }
+
     return array('target_id' => $element);
   }
 
@@ -178,12 +182,13 @@ protected function getAutocreateBundle() {
       if (($target_bundles = $this->getSelectionHandlerSetting('target_bundles')) && count($target_bundles) == 1) {
         $bundle = reset($target_bundles);
       }
-      // Otherwise try to see if the entity type has a single bundle and use it.
-      elseif (($bundles = entity_get_bundles($this->getFieldSetting('target_type'))) && count($bundles) == 1) {
+      // Otherwise use the first bundle as a fallback.
+      else {
+        // @todo Expose a proper UI for choosing the bundle for autocreated
+        // entities in https://www.drupal.org/node/2412569.
+        $bundles = entity_get_bundles($this->getFieldSetting('target_type'));
         $bundle = key($bundles);
       }
-      // @todo Expose a proper UI for choosing the bundle for autocreated
-      // entities in https://www.drupal.org/node/2412569.
     }
 
     return $bundle;
diff --git a/core/modules/system/src/Controller/EntityAutocompleteController.php b/core/modules/system/src/Controller/EntityAutocompleteController.php
index 071941e..bd47031 100644
--- a/core/modules/system/src/Controller/EntityAutocompleteController.php
+++ b/core/modules/system/src/Controller/EntityAutocompleteController.php
@@ -10,7 +10,7 @@
 use Drupal\Component\Utility\Tags;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Controller\ControllerBase;
-use Drupal\system\EntityAutocompleteMatcher;
+use Drupal\Core\Entity\EntityAutocompleteMatcher;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Request;
@@ -21,17 +21,17 @@
 class EntityAutocompleteController extends ControllerBase {
 
   /**
-   * The autocomplete helper for entity references.
+   * The autocomplete matcher for entity references.
    *
-   * @var \Drupal\system\EntityAutocompleteMatcher
+   * @var \Drupal\Core\Entity\EntityAutocompleteMatcher
    */
   protected $entityAutocompleteMatcher;
 
   /**
    * Constructs a EntityAutocompleteController object.
    *
-   * @param \Drupal\system\EntityAutocompleteMatcher $entity_autocomplete_matcher
-   *   The autocompletion helper for entity references.
+   * @param \Drupal\Core\Entity\EntityAutocompleteMatcher $entity_autocomplete_matcher
+   *   The autocomplete matcher for entity references.
    */
   public function __construct(EntityAutocompleteMatcher $entity_autocomplete_matcher) {
     $this->entityAutocompleteMatcher = $entity_autocomplete_matcher;
@@ -59,7 +59,7 @@ public static function create(ContainerInterface $container) {
    *   The settings that will be passed to the selection handler.
    *
    * @return \Symfony\Component\HttpFoundation\JsonResponse
-   *   The matched entity labels as JSON.
+   *   The matched entity labels as a JSON response.
    */
   public function handleAutocomplete(Request $request, $target_type, $selection_handler, $selection_settings = '') {
     $matches = array();
diff --git a/core/modules/user/src/Tests/UserEntityReferenceTest.php b/core/modules/user/src/Tests/UserEntityReferenceTest.php
index 81645b2..215bf98 100644
--- a/core/modules/user/src/Tests/UserEntityReferenceTest.php
+++ b/core/modules/user/src/Tests/UserEntityReferenceTest.php
@@ -79,7 +79,7 @@ function testUserSelectionByRole() {
     $user3->save();
 
 
-    /** @var \Drupal\system\EntityAutocompleteMatcher $autocomplete */
+    /** @var \Drupal\Core\Entity\EntityAutocompleteMatcher $autocomplete */
     $autocomplete = \Drupal::service('entity.autocomplete_matcher');
 
     $matches = $autocomplete->getMatches('user', 'default', $field_definition->getSetting('handler_settings'), 'aabb');