diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index f87c79a..1beb719 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -521,27 +521,19 @@ function simpletest_classloader_register() {
     'theme' => array('dir' => 'themes', 'extension' => 'info'),
     'profile' => array('dir' => 'profiles', 'extension' => 'profile'),
   );
+  $loader = drupal_classloader();
   foreach ($types as $type => $info) {
     $matches = drupal_system_listing('/^' . DRUPAL_PHP_FUNCTION_PATTERN . '\.' . $info['extension'] . '$/', $info['dir']);
     foreach ($matches as $name => $file) {
-      drupal_classloader()->addDrupalExtension($name, dirname($file->uri));
-      drupal_classloader()->addDrupalExtensionTests($name, dirname($file->uri));
+      $loader->addDrupalExtension($name, dirname($file->uri));
+      $loader->addDrupalExtensionTests($name, dirname($file->uri));
       // While being there, prime drupal_get_filename().
       drupal_get_filename($type, $name, $file->uri);
     }
   }
 
   // Register the core test directory so we can find \Drupal\UnitTestCase.
-  drupal_classloader()->add('Drupal\\Tests\\', DRUPAL_ROOT . '/core/tests');
-
-  // Manually register phpunit prefixes because they use a classmap instead of a
-  // prefix. This can be safely removed if we move to using composer's
-  // autoloader with a classmap.
-  drupal_classloader()->addMultiple(array(
-    'PHPUnit' => DRUPAL_ROOT . '/core/vendor/phpunit/phpunit',
-    'File_Iterator' => DRUPAL_ROOT . '/core/vendor/phpunit/php-file-iterator/',
-    'PHP_Timer' => DRUPAL_ROOT . '/core/vendor/phpunit/php-timer/',
-  ));
+  $loader->add('Drupal\\Tests\\', DRUPAL_ROOT . '/core/tests');
 }
 
 /**