diff --git a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
index 9fdc7c5..1089aa8 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -144,6 +144,15 @@
   protected $originalSettings;
 
   /**
+   * The public file directory for the test environment.
+   *
+   * This is set in TestBase::prepareEnvironment().
+   *
+   * @var string
+   */
+  protected $public_files_directory;
+
+  /**
    * TRUE if die on fail enabled.
    *
    * @var boolean
diff --git a/core/modules/system/lib/Drupal/system/Tests/DrupalKernel/DrupalKernelTest.php b/core/modules/system/lib/Drupal/system/Tests/DrupalKernel/DrupalKernelTest.php
index cc84777..9e869ee 100644
--- a/core/modules/system/lib/Drupal/system/Tests/DrupalKernel/DrupalKernelTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/DrupalKernel/DrupalKernelTest.php
@@ -32,7 +32,7 @@ function setUp() {
     $conf['php_storage']['service_container']= array(
       'bin' => 'service_container',
       'class' => 'Drupal\Component\PhpStorage\MTimeProtectedFileStorage',
-      'directory' => DRUPAL_ROOT . '/' . config('system.file')->get('path.public') . '/php',
+      'directory' => DRUPAL_ROOT . '/' . $this->public_files_directory . '/php',
       'secret' => $GLOBALS['drupal_hash_salt'],
     );
     // Use a non-persistent cache to avoid queries to non-existing tables.