diff --git a/core/modules/system/lib/Drupal/system/Tests/Common/RenderTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/RenderTest.php
index 14ce926..bd388a6 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Common/RenderTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/RenderTest.php
@@ -858,7 +858,7 @@ function testDrupalRenderRenderCachePlaceholder() {
    * element.
    */
   function testDrupalRenderChildElementRenderCachePlaceholder() {
-    $context = array('bar' => $this->randomString());
+    $context = array('bar' => $this->randomContextValue());
     $container = array(
       '#type' => 'container',
     );