diff --git a/core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php b/core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
index 8a95237..0862caf 100644
--- a/core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
+++ b/core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
@@ -30,6 +30,7 @@ public function getInfo() {
     $info['#target_type'] = NULL;
     $info['#selection_handler'] = 'default';
     $info['#selection_settings'] = array();
+    $info['#validate_reference'] = TRUE;
     $info['#tags'] = FALSE;
     $info['#autocreate'] = NULL;
 
@@ -77,7 +78,7 @@ public static function processEntityAutocomplete(&$element, FormStateInterface $
         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();
+      $element['#autocreate']['uid'] = isset($element['#autocreate']['uid']) ? $element['#autocreate']['uid'] : \Drupal::currentUser()->id();
     }
 
     $element['#autocomplete_route_name'] = 'system.entity_autocomplete';
@@ -134,6 +135,25 @@ public static function validateEntityAutocomplete(&$element, FormStateInterface
         }
       }
 
+      // Check that the referenced entities are valid, if needed.
+      if ($element['#validate_reference'] && !$autocreate && !empty($value)) {
+        $ids = array_reduce($value, function ($return, $item) {
+          if (isset($item['target_id'])) {
+            $return[] = $item['target_id'];
+          }
+          return $return;
+        });
+
+        if ($ids) {
+          $valid_ids = $handler->validateReferenceableEntities($ids);
+          if ($invalid_ids = array_diff($ids, $valid_ids)) {
+            foreach ($invalid_ids as $invalid_id) {
+              $form_state->setError($element, t('The referenced entity (%type: %id) does not exist.', array('%type' => $element['#target_type'], '%id' => $invalid_id)));
+            }
+          }
+        }
+      }
+
       // Use only the last value if the form element does not support multiple
       // matches (tags).
       if (!$element['#tags'] && !empty($value)) {
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 bc646ec..0be6656 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/AutocompleteWidget.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/AutocompleteWidget.php
@@ -100,6 +100,9 @@ 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'),
+      // Entiy reference field items are handling validation themselves via
+      // the 'ValidReference' constraint.
+      '#validate_reference' => FALSE,
       '#maxlength' => 1024,
       '#default_value' => implode(', ', $this->getLabels($items, $delta)),
       '#size' => $this->getSetting('size'),
diff --git a/core/modules/system/src/Tests/Entity/Element/EntityAutocompleteElementFormTest.php b/core/modules/system/src/Tests/Entity/Element/EntityAutocompleteElementFormTest.php
new file mode 100644
index 0000000..d7d0dc1
--- /dev/null
+++ b/core/modules/system/src/Tests/Entity/Element/EntityAutocompleteElementFormTest.php
@@ -0,0 +1,292 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Entity\Element\EntityAutocompleteElementFormTest.
+ */
+
+namespace Drupal\system\Tests\Entity\Element;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormInterface;
+use Drupal\Core\Form\FormState;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\system\Tests\Entity\EntityUnitTestBase;
+use Drupal\user\Entity\User;
+
+/**
+ * Tests the EntityAutocomplete Form API element.
+ *
+ * @group Form
+ */
+class EntityAutocompleteElementFormTest extends EntityUnitTestBase implements FormInterface {
+
+  /**
+   * User for testing.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $testUser;
+
+  /**
+   * User for autocreate testing.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $testAutocreateUser;
+
+  /**
+   * An array of entities to be referenced in this test.
+   *
+   * @var \Drupal\Core\Entity\EntityInterface[]
+   */
+  protected $referencedEntities;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installSchema('system', array('router'));
+    \Drupal::service('router.builder')->rebuild();
+
+    $this->testUser = User::create(array(
+      'name' => 'foobar1',
+      'mail' => 'foobar1@example.com',
+    ));
+    $this->testUser->save();
+    \Drupal::service('current_user')->setAccount($this->testUser);
+
+    $this->testAutocreateUser = User::create(array(
+      'name' => 'foobar2',
+      'mail' => 'foobar2@example.com',
+    ));
+    $this->testAutocreateUser->save();
+
+    for ($i = 1; $i < 3; $i++) {
+      $entity = EntityTest::create(array(
+        'name' => $this->randomMachineName()
+      ));
+      $entity->save();
+      $this->referencedEntities[] = $entity;
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'test_entity_autocomplete';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['single'] = array(
+      '#type' => 'entity_autocomplete',
+      '#target_type' => 'entity_test',
+    );
+    $form['single_autocreate'] = array(
+      '#type' => 'entity_autocomplete',
+      '#target_type' => 'entity_test',
+      '#autocreate' => array(
+        'bundle' => 'entity_test',
+      ),
+    );
+    $form['single_autocreate_specific_uid'] = array(
+      '#type' => 'entity_autocomplete',
+      '#target_type' => 'entity_test',
+      '#autocreate' => array(
+        'bundle' => 'entity_test',
+        'uid' => $this->testAutocreateUser->id(),
+      ),
+    );
+
+    $form['tags'] = array(
+      '#type' => 'entity_autocomplete',
+      '#target_type' => 'entity_test',
+      '#tags' => TRUE,
+    );
+    $form['tags_autocreate'] = array(
+      '#type' => 'entity_autocomplete',
+      '#target_type' => 'entity_test',
+      '#tags' => TRUE,
+      '#autocreate' => array(
+        'bundle' => 'entity_test',
+      ),
+    );
+    $form['tags_autocreate_specific_uid'] = array(
+      '#type' => 'entity_autocomplete',
+      '#target_type' => 'entity_test',
+      '#tags' => TRUE,
+      '#autocreate' => array(
+        'bundle' => 'entity_test',
+        'uid' => $this->testAutocreateUser->id(),
+      ),
+    );
+
+    $form['single_no_validate'] = array(
+      '#type' => 'entity_autocomplete',
+      '#target_type' => 'entity_test',
+      '#validate_reference' => FALSE,
+    );
+    $form['single_autocreate_no_validate'] = array(
+      '#type' => 'entity_autocomplete',
+      '#target_type' => 'entity_test',
+      '#autocreate' => array(
+        'bundle' => 'entity_test',
+      ),
+    );
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) { }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) { }
+
+  /**
+   * Tests valid entries in the EntityAutocomplete Form API element.
+   */
+  public function testValidEntityAutocompleteElement() {
+    $form_state = (new FormState())
+      ->setValues([
+        'single' => $this->getAutocompleteInput($this->referencedEntities[0]),
+        'single_autocreate' => 'single - autocreated entity label',
+        'single_autocreate_specific_uid' => 'single - autocreated entity label with specific uid',
+        'tags' => $this->getAutocompleteInput($this->referencedEntities[0]) . ', ' . $this->getAutocompleteInput($this->referencedEntities[1]),
+        'tags_autocreate' =>
+          $this->getAutocompleteInput($this->referencedEntities[0])
+          . ', tags - autocreated entity label, '
+          . $this->getAutocompleteInput($this->referencedEntities[1]),
+        'tags_autocreate_specific_uid' =>
+          $this->getAutocompleteInput($this->referencedEntities[0])
+          . ', tags - autocreated entity label with specific uid, '
+          . $this->getAutocompleteInput($this->referencedEntities[1]),
+      ]);
+    $form_builder = $this->container->get('form_builder');
+    $form_builder->submitForm($this, $form_state);
+
+    // Valid form state.
+    $this->assertEqual(count($form_state->getErrors()), 0);
+
+    // Test the 'single' element.
+    $this->assertEqual($form_state->getValue('single'), $this->referencedEntities[0]->id());
+
+    // Test the 'single_autocreate' element.
+    $value = $form_state->getValue('single_autocreate');
+    $this->assertEqual($value['entity']->label(), 'single - autocreated entity label');
+    $this->assertEqual($value['entity']->bundle(), 'entity_test');
+    $this->assertEqual($value['entity']->getOwnerId(), $this->testUser->id());
+
+    // Test the 'single_autocreate_specific_uid' element.
+    $value = $form_state->getValue('single_autocreate_specific_uid');
+    $this->assertEqual($value['entity']->label(), 'single - autocreated entity label with specific uid');
+    $this->assertEqual($value['entity']->bundle(), 'entity_test');
+    $this->assertEqual($value['entity']->getOwnerId(), $this->testAutocreateUser->id());
+
+    // Test the 'tags' element.
+    $expected = array(
+      array('target_id' => $this->referencedEntities[0]->id()),
+      array('target_id' => $this->referencedEntities[1]->id()),
+    );
+    $this->assertEqual($form_state->getValue('tags'), $expected);
+
+    // Test the 'single_autocreate' element.
+    $value = $form_state->getValue('tags_autocreate');
+    // First value is an existing entity.
+    $this->assertEqual($value[0]['target_id'], $this->referencedEntities[0]->id());
+    // Second value is an autocreated entity.
+    $this->assertTrue(!isset($value[1]['target_id']));
+    $this->assertEqual($value[1]['entity']->label(), 'tags - autocreated entity label');
+    $this->assertEqual($value[1]['entity']->getOwnerId(), $this->testUser->id());
+    // Third value is an existing entity.
+    $this->assertEqual($value[2]['target_id'], $this->referencedEntities[1]->id());
+
+    // Test the 'tags_autocreate_specific_uid' element.
+    $value = $form_state->getValue('tags_autocreate_specific_uid');
+    // First value is an existing entity.
+    $this->assertEqual($value[0]['target_id'], $this->referencedEntities[0]->id());
+    // Second value is an autocreated entity.
+    $this->assertTrue(!isset($value[1]['target_id']));
+    $this->assertEqual($value[1]['entity']->label(), 'tags - autocreated entity label with specific uid');
+    $this->assertEqual($value[1]['entity']->getOwnerId(), $this->testAutocreateUser->id());
+    // Third value is an existing entity.
+    $this->assertEqual($value[2]['target_id'], $this->referencedEntities[1]->id());
+  }
+
+  /**
+   * Tests invalid entries in the EntityAutocomplete Form API element.
+   */
+  public function testInvalidEntityAutocompleteElement() {
+    $form_builder = $this->container->get('form_builder');
+
+    // Test 'single' with a entity label that doesn't exist
+    $form_state = (new FormState())
+      ->setValues([
+        'single' => 'single - inexistent label',
+      ]);
+    $form_builder->submitForm($this, $form_state);
+    $this->assertEqual(count($form_state->getErrors()), 1);
+    $this->assertEqual($form_state->getErrors()['single'], t('There are no entities matching "%value".', array('%value' => 'single - inexistent label')));
+
+    // Test 'single' with a entity ID that doesn't exist.
+    $form_state = (new FormState())
+      ->setValues([
+        'single' => 'single - inexistent label (42)',
+      ]);
+    $form_builder->submitForm($this, $form_state);
+    $this->assertEqual(count($form_state->getErrors()), 1);
+    $this->assertEqual($form_state->getErrors()['single'], t('The referenced entity (%type: %id) does not exist.', array('%type' => 'entity_test', '%id' => 42)));
+
+    // Do the same tests as above but on an element with '#validate_reference'
+    // set to FALSE.
+    $form_state = (new FormState())
+      ->setValues([
+        'single_no_validate' => 'single - inexistent label',
+        'single_autocreate_no_validate' => 'single - autocreate inexistent label'
+      ]);
+    $form_builder->submitForm($this, $form_state);
+
+    // The element without 'autocreate' support still has to emit a warning when
+    // the input doesn't end with an entity ID enclosed in parentheses.
+    $this->assertEqual(count($form_state->getErrors()), 1);
+    $this->assertEqual($form_state->getErrors()['single_no_validate'], t('There are no entities matching "%value".', array('%value' => 'single - inexistent label')));
+
+    $form_state = (new FormState())
+      ->setValues([
+        'single_no_validate' => 'single - inexistent label (42)',
+        'single_autocreate_no_validate' => 'single - autocreate inexistent label (43)'
+      ]);
+    $form_builder->submitForm($this, $form_state);
+
+    // The input is complete (i.e. contains an entity ID at the ent), no errors
+    // are triggered.
+    $this->assertEqual(count($form_state->getErrors()), 0);
+  }
+
+
+  /**
+   * Returns an entity label in the format needed by the EntityAutocomplete
+   * element.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   A Drupal entity.
+   *
+   * @return string
+   *   A string that can be used as a value for EntityAutocomplete elements.
+   */
+  protected function getAutocompleteInput(EntityInterface $entity) {
+    return $entity->label() . ' (' . $entity->id() . ')';
+  }
+
+}