diff --git a/core/includes/install.inc b/core/includes/install.inc
index 5c0abcab8e..699c174151 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -533,6 +533,7 @@ function drupal_install_config_directories() {
  *   config_get_config_directory() and file_prepare_directory() instead.
  */
 function install_ensure_config_directory($type) {
+  @trigger_error('install_ensure_config_directory() is deprecated in Drupal 8.1.0 and will be removed before Drupal 9.0.0. Use config_get_config_directory() and file_prepare_directory() instead. See https://www.drupal.org/node/2501187.', E_USER_DEPRECATED);
   // The config directory must be defined in settings.php.
   global $config_directories;
   if (!isset($config_directories[$type])) {
diff --git a/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
index b133bfb2fb..ff15c39ac4 100644
--- a/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -121,7 +121,7 @@ protected function prepareConfigDirectories() {
     $path = $this->siteDirectory . '/config_' . CONFIG_SYNC_DIRECTORY;
     $GLOBALS['config_directories'][CONFIG_SYNC_DIRECTORY] = $path;
     // Ensure the directory can be created and is writeable.
-    if (!install_ensure_config_directory(CONFIG_SYNC_DIRECTORY)) {
+    if (!file_prepare_directory($path, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS)) {
       throw new \RuntimeException("Failed to create '" . CONFIG_SYNC_DIRECTORY . "' config directory $path");
     }
     // Provide the already resolved path for tests.