diff --git a/core/lib/Drupal/Core/Form/ConfigFormBaseTrait.php b/core/lib/Drupal/Core/Form/ConfigFormBaseTrait.php
index 1cbac3c..fa74a47 100644
--- a/core/lib/Drupal/Core/Form/ConfigFormBaseTrait.php
+++ b/core/lib/Drupal/Core/Form/ConfigFormBaseTrait.php
@@ -41,8 +41,10 @@
    *   the config object returned will contain the contents of book.admin
    *   configuration file.
    *
-   * @return \Drupal\Core\Config\Config|\Drupal\Core\Config\ImmutableConfig
-   *   A configuration object.
+   * @return \Drupal\Core\Config\Config|\Drupal\Core\Config\Config|\Drupal\Core\Config\ImmutableConfig
+   *   An editable configuration object if the given name is listed in the
+   *   getEditableConfigNames() method or an immutable configuration object if
+   *   not.
    */
   protected function config($name) {
     /** @var \Drupal\Core\Config\ConfigFactoryInterface $config_factory */