diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 6bd8dd4..4b8c1a5 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1372,7 +1372,8 @@ function system_sort_modules_by_info_name($a, $b) {
 }
 
 /**
- * Sorts themes by their name.
+ * Sorts themes with the default theme first, and then by name within the other
+ * non-default themes.
  *
  * Callback for uasort() within
  * \Drupal\system\Controller\SystemController::themesPage().