diff --git a/core/modules/system/src/Tests/System/HtaccessTest.php b/core/modules/system/src/Tests/System/HtaccessTest.php
index 3335033..29f133d 100644
--- a/core/modules/system/src/Tests/System/HtaccessTest.php
+++ b/core/modules/system/src/Tests/System/HtaccessTest.php
@@ -21,10 +21,20 @@ class HtaccessTest extends WebTestBase {
    */
   public function testYamlFileAccess() {
     // Try accessing the core services YAML file.
-    $this->drupalGet('core/core.services.yml');
-    $this->assertResponse(403);
+    $this->assertNoFileAccess('core/core.services.yml');
     // Try accessing a core module YAML file.
-    $this->drupalGet('core/modules/system/system.services.yml');
+    $this->assertNoFileAccess('core/modules/system/system.services.yml');
+  }
+
+  /**
+   * Asserts that a file exists but not accessible via HTTP.
+   *
+   * @param $path
+   *   Path to file. Without leading slash.
+   */
+  protected function assertNoFileAccess($path) {
+    $this->assertTrue(file_exists(DRUPAL_ROOT . '/' . $path));
+    $this->drupalGet($path);
     $this->assertResponse(403);
   }