diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 3025b64..6220cdf 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -101,8 +101,8 @@
  *
  * @see config_get_config_directory()
  *
- * @deprecated Drupal 8.0.0 no longer creates an active directory. This will be
- *   removed in Drupal 9.0.x
+ * @deprecated in Drupal 8.0.x and will be removed before 9.0.0. Drupal core no
+ *   longer creates an active directory.
  */
 const CONFIG_ACTIVE_DIRECTORY = 'active';
 
@@ -164,14 +164,17 @@ function conf_path($require_settings = TRUE, $reset = FALSE, Request $request =
 /**
  * Returns the path of a configuration directory.
  *
+ * Configuration directories are configured using $config_directories in
+ * settings.php.
+ *
  * @param string $type
- *   (optional) The type of config directory to return. Drupal core provides
- *   'staging'. Defaults to CONFIG_ACTIVE_DIRECTORY.
+ *   The type of config directory to return. Drupal core provides the
+ *   CONFIG_STAGING_DIRECTORY constant to access the staging directory.
  *
  * @return string
  *   The configuration directory path.
  */
-function config_get_config_directory($type = CONFIG_ACTIVE_DIRECTORY) {
+function config_get_config_directory($type) {
   global $config_directories;
 
   if (!empty($config_directories[$type])) {
diff --git a/core/modules/config/src/Tests/ConfigImporterTest.php b/core/modules/config/src/Tests/ConfigImporterTest.php
index c830b45..816fb4f 100644
--- a/core/modules/config/src/Tests/ConfigImporterTest.php
+++ b/core/modules/config/src/Tests/ConfigImporterTest.php
@@ -648,4 +648,21 @@ public function testMissingCoreExtension() {
     }
   }
 
+  /**
+   * Tests config_get_config_directory().
+   */
+  public function testConfigGetConfigDirectory() {
+    $directory = config_get_config_directory(CONFIG_STAGING_DIRECTORY);
+    $this->assertEqual($this->configDirectories[CONFIG_STAGING_DIRECTORY], $directory);
+
+    $message = 'Calling config_get_config_directory() with CONFIG_ACTIVE_DIRECTORY results in an exception.';
+    try {
+      config_get_config_directory(CONFIG_ACTIVE_DIRECTORY);
+      $this->fail($message);
+    }
+    catch (\Exception $e) {
+      $this->pass($message);
+    }
+  }
+
 }