diff -u b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
--- b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
+++ b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
@@ -32,7 +32,7 @@
    *   The directory to scan in each extension to scan for files. Defaults to
    *   'config'.
    */
-  public function __construct(StorageInterface $config_storage, $directory = 'config/install') {
+  public function __construct(StorageInterface $config_storage, $directory = self::CONFIG_INSTALL_DIRECTORY) {
     $this->configStorage = $config_storage;
     $this->directory = $directory;
   }
diff -u b/core/lib/Drupal/Core/Config/InstallStorage.php b/core/lib/Drupal/Core/Config/InstallStorage.php
--- b/core/lib/Drupal/Core/Config/InstallStorage.php
+++ b/core/lib/Drupal/Core/Config/InstallStorage.php
@@ -23,6 +23,16 @@
 class InstallStorage extends FileStorage {
 
   /**
+   * Extension sub-directory containing default configuration for installation.
+   */
+  const CONFIG_INSTALL_DIRECTORY = 'config/install';
+
+  /**
+   * Extension sub-directory containing configuration schema.
+   */
+  const CONFIG_SCHEMA_DIRECTORY = 'config/schema';
+
+  /**
    * Folder map indexed by configuration name.
    *
    * @var array
@@ -43,7 +53,7 @@
    *   The directory to scan in each extension to scan for files. Defaults to
    *   'config'.
    */
-  public function __construct($directory = 'config/install') {
+  public function __construct($directory = self::CONFIG_INSTALL_DIRECTORY) {
     $this->directory = $directory;
   }
 
diff -u b/core/lib/Drupal/Core/Extension/UpdateModuleHandler.php b/core/lib/Drupal/Core/Extension/UpdateModuleHandler.php
--- b/core/lib/Drupal/Core/Extension/UpdateModuleHandler.php
+++ b/core/lib/Drupal/Core/Extension/UpdateModuleHandler.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Config\ConfigException;
 use Drupal\Core\Config\FileStorage;
+use Drupal\Core\Config\InstallStorage;
 
 /**
  * Deals with module enables and throws exception if hooks fired during updates.
@@ -103,7 +104,7 @@
       // The default configuration is not altered in any way, and since the module
       // is just being installed, none of its configuration can exist already, so
       // this is a plain copy operation from one storage to another.
-      $module_config_path = drupal_get_path('module', $module) . '/config/install';
+      $module_config_path = drupal_get_path('module', $module) . '/'. InstallStorage::CONFIG_INSTALL_DIRECTORY;
       if (is_dir($module_config_path)) {
         $module_filestorage = new FileStorage($module_config_path);
         $config_storage = \Drupal::service('config.storage');
diff -u b/core/modules/config/lib/Drupal/config/Tests/ConfigInstallWebTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigInstallWebTest.php
--- b/core/modules/config/lib/Drupal/config/Tests/ConfigInstallWebTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigInstallWebTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\config\Tests;
 
+use Drupal\Core\Config\InstallStorage;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Config\FileStorage;
 
@@ -122,7 +123,7 @@
     // Verify that the original data matches. We have to read the module config
     // file directly, because the install profile default system.cron.yml
     // configuration file was used to create the active configuration.
-    $config_dir = drupal_get_path('module', 'system') . '/config/install';
+    $config_dir = drupal_get_path('module', 'system') . '/'. InstallStorage::CONFIG_INSTALL_DIRECTORY;
     $this->assertTrue(is_dir($config_dir));
     $source_storage = new FileStorage($config_dir);
     $data = $source_storage->read($config_name);
diff -u b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleTestBase.php
--- b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleTestBase.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\system\Tests\Module;
 
+use Drupal\Core\Config\InstallStorage;
 use Drupal\Core\Database\Database;
 use Drupal\Core\Config\FileStorage;
 use Drupal\simpletest\WebTestBase;
@@ -95,7 +96,7 @@
    *   TRUE if configuration has been installed, FALSE otherwise.
    */
   function assertModuleConfig($module) {
-    $module_config_dir = drupal_get_path('module', $module) . '/config/install';
+    $module_config_dir = drupal_get_path('module', $module) . '/'. InstallStorage::CONFIG_INSTALL_DIRECTORY;
     if (!is_dir($module_config_dir)) {
       return;
     }
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Config/ConfigManager.php
+++ b/core/lib/Drupal/Core/Config/ConfigManager.php
@@ -156,7 +156,7 @@ public function uninstall($type, $name) {
     foreach ($config_names as $config_name) {
       $this->configFactory->get($config_name)->delete();
     }
-    $schema_dir = drupal_get_path($type, $name) . '/config/schema';
+    $schema_dir = drupal_get_path($type, $name) . '/' . InstallStorage::CONFIG_SCHEMA_DIRECTORY;
     if (is_dir($schema_dir)) {
       // Refresh the schema cache if uninstalling an extension that provides
       // configuration schema.
only in patch2:
unchanged:
--- a/core/modules/config/lib/Drupal/config/Tests/DefaultConfigTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/DefaultConfigTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\config\Tests;
 
 use Drupal\config_test\TestInstallStorage;
+use Drupal\Core\Config\InstallStorage;
 use Drupal\Core\Config\Schema\Property;
 use Drupal\Core\Config\TypedConfigManager;
 use Drupal\Core\TypedData\Type\BooleanInterface;
@@ -69,7 +70,7 @@ public function testDefaultConfig() {
     // every module, profile and theme.
     $typed_config = new TypedConfigManager(
       \Drupal::service('config.storage'),
-      new TestInstallStorage('config/schema'),
+      new TestInstallStorage(InstallStorage::CONFIG_SCHEMA_DIRECTORY),
       \Drupal::service('cache.config')
     );