diff --git a/core/includes/install.inc b/core/includes/install.inc
index 28336be..e6598f2 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -532,6 +532,9 @@ function drupal_install_config_directories() {
  *
  * @return bool
  *   TRUE if the config directory exists and is writable.
+ *
+ * @deprecated in Drupal 8.1.x, will be removed before Drupal 9.0.x. Use
+ *   config_get_config_directory() and file_prepare_directory() instead.
  */
 function install_ensure_config_directory($type) {
   // The config directory must be defined in settings.php.