diff --git a/core/lib/Drupal/Core/Extension/ThemeHandler.php b/core/lib/Drupal/Core/Extension/ThemeHandler.php
index 9398072..2d8ee1f 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandler.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandler.php
@@ -433,6 +433,12 @@ protected function doGetBaseThemes(array $themes, $theme, $used_themes = array()
     return $current_base_theme;
   }
 
+  /**
+   * Returns a system listing info object.
+   *
+   * @return \Drupal\Core\SystemListingInfo
+   *   The system listing object.
+   */
   protected function getSystemListingInfo() {
     if (!isset($this->systemListingInfo)) {
       $this->systemListingInfo = new SystemListingInfo();