diff --git a/core/modules/user/lib/Drupal/user/Tests/UserAutocompleteTest.php b/core/modules/user/lib/Drupal/user/Tests/UserAutocompleteTest.php
index d225150d691..5679b185d0f 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserAutocompleteTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserAutocompleteTest.php
@@ -46,5 +46,13 @@ class UserAutocompleteTest extends WebTestBase {
 
     // Using first letter of the user's name, make sure the user's full name is in the results.
     $this->assertRaw($this->unprivileged_user->name, 'User name found in autocompletion results.');
+
+    // Test that anonymous username is in the result.
+    $anonymous_name = $this->randomString();
+    config('user.settings')->set('anonymous', $anonymous_name)->save();
+    $this->drupalGet('user/autocomplete', array('query' => array('q' => drupal_substr($anonymous_name, 0, 4), 'anonymous' => '1')));
+    $this->assertRaw($anonymous_name, 'The anonymous name found in autocompletion results.');
+    $this->drupalGet('user/autocomplete', array('query' => array('q' => drupal_substr($anonymous_name, 0, 4))));
+    $this->assertNoRaw($anonymous_name, 'The anonymous name not found in autocompletion results without enabling anonymous username.');
   }
 }
diff --git a/core/modules/user/user.pages.inc b/core/modules/user/user.pages.inc
index c1b93496a8a..87408f10fec 100644
--- a/core/modules/user/user.pages.inc
+++ b/core/modules/user/user.pages.inc
@@ -12,11 +12,31 @@ use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
 use Symfony\Component\HttpKernel\HttpKernelInterface;
 
 /**
- * Menu callback; Retrieve a JSON object containing autocomplete suggestions for existing users.
+ * Menu callback for user autocompletion.
+ *
+ * Like other autocomplete functions, this function inspects the 'q' query
+ * parameter for the string to use to search for suggestions. If the name used
+ * to indicate anonymous users (e.g. "Anonymous") is to be included as a
+ * possible suggestion, the 'anonymous' query parameter should be set
+ * additionally. For example, http://example.com/user/autocomplete?q=An might
+ * return "Andrew" and "Anne", while
+ * http://example.com/user/autocomplete?q=An&anonymous=1 will additionally
+ * return "Anonymous".
+ *
+ * @return \Symfony\Component\HttpFoundation\JsonResponse
+ *   A JSON response containing the autocomplete suggestions for existing users.
  */
 function user_autocomplete() {
   $matches = array();
-  if ($string = drupal_container()->get('request')->query->get('q')) {
+  $query = drupal_container()->get('request')->query;
+  if ($string = $query->get('q')) {
+    if ($query->get('anonymous')) {
+      $anonymous_name = config('user.settings')->get('anonymous');
+      // Allow autocompletion for the anonymous user.
+      if (stripos($anonymous_name, $string) !== FALSE) {
+        $matches[$anonymous_name] = check_plain($anonymous_name);
+      }
+    }
     $result = db_select('users')->fields('users', array('name'))->condition('name', db_like($string) . '%', 'LIKE')->range(0, 10)->execute();
     foreach ($result as $account) {
       $matches[$account->name] = check_plain($account->name);