diff --git a/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
index c2d3ab1..99c573a 100644
--- a/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -477,6 +477,7 @@ public function escapeFilter(\Twig_Environment $env, $arg, $strategy = 'html', $
    *
    * When $arg is passed as an object which does not implement __toString(),
    * RenderableInterface or toString(). Other objects are casted to string.
+   * If it already implements __toString(), it will throw an exception.
    * However in the case that the object is an instance of a Twig_Markup object
    * it is returned directly to support auto escaping.
    *