diff --git a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
index 01c1bc5..89589d9 100644
--- a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Tests\Core\Template;
 
+use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Core\Render\RenderableInterface;
 use Drupal\Core\Render\RendererInterface;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
@@ -173,6 +174,11 @@ public function testSafeJoin() {
     ];
     $result = $twig_extension->safeJoin($twig_environment, $items, '<br/>');
     $this->assertEquals('&lt;em&gt;will be escaped&lt;/em&gt;<br/><em>will be markup</em><br/><strong>will be rendered</strong>', $result);
+
+    // Ensure that result of safe join can be used in t() and string formatting
+    // without double escaping.
+    $result = new FormattableMarkup('Kittens @text', ['@text' => $result]);
+    $this->assertEquals('Kittens &lt;em&gt;will be escaped&lt;/em&gt;<br/><em>will be markup</em><br/><strong>will be rendered</strong>', $result);
   }
 
   /**