diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 1b6c8a3..b1831d5 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -337,7 +337,7 @@ function install_begin_request(&$install_state) {
   // because any data put in the cache during the installer is inherently
   // suspect, due to the fact that Drupal is not fully set up yet.
   require_once DRUPAL_ROOT . '/core/includes/cache.inc';
-  $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\InstallBackend');
+  $GLOBALS['cache_classes'] = array('cache' => 'Drupal\Core\Cache\InstallBackend');
 
   // The install process cannot use the database lock backend since the database
   // is not fully up, so we use a null backend implementation during the
diff --git a/core/lib/Drupal/Core/Cache/CacheBackendInterface.php b/core/lib/Drupal/Core/Cache/CacheBackendInterface.php
index 2140960..94d58e8 100644
--- a/core/lib/Drupal/Core/Cache/CacheBackendInterface.php
+++ b/core/lib/Drupal/Core/Cache/CacheBackendInterface.php
@@ -20,20 +20,20 @@
  * Drupal\Core\Cache\CacheBackendInterface was called MyCustomCache, the
  * following line would make Drupal use it for the 'cache_page' bin:
  * @code
- *  $conf['cache_classes']['cache_page'] = 'MyCustomCache';
+ *  $cache_classes['cache_page'] = 'MyCustomCache';
  * @endcode
  *
  * Additionally, you can register your cache implementation to be used by
- * default for all cache bins by setting the $conf['cache_classes'] variable and
+ * default for all cache bins by setting the $cache_classes variable and
  * changing the value of the 'cache' key to the name of your implementation of
  * the Drupal\Core\Cache\CacheBackendInterface, e.g.
  * @code
- *  $conf['cache_classes']['cache'] = 'MyCustomCache';
+ *  $cache_classes['cache'] = 'MyCustomCache';
  * @endcode
  *
  * To implement a completely custom cache bin, use the same variable format:
  * @code
- *  $conf['cache_classes']['custom_bin'] = 'MyCustomCache';
+ *  $cache_classes['custom_bin'] = 'MyCustomCache';
  * @endcode
  * To access your custom cache bin, specify the name of the bin when storing
  * or retrieving cached data:
diff --git a/core/lib/Drupal/Core/Cache/CacheFactory.php b/core/lib/Drupal/Core/Cache/CacheFactory.php
index da42a26..09bcdde 100644
--- a/core/lib/Drupal/Core/Cache/CacheFactory.php
+++ b/core/lib/Drupal/Core/Cache/CacheFactory.php
@@ -46,8 +46,8 @@ public static function getBackends() {
     // @todo Improve how cache backend classes are defined. Cannot be
     //   configuration, since e.g. the CachedStorage config storage controller
     //   requires the definition in its constructor already.
-    global $conf;
-    $cache_backends = isset($conf['cache_classes']) ? $conf['cache_classes'] : array();
+    global $cache_classes;
+    $cache_backends = isset($cache_classes) ? $cache_classes : array();
     // Ensure there is a default 'cache' bin definition.
     $cache_backends += array('cache' => 'Drupal\Core\Cache\DatabaseBackend');
     return $cache_backends;