diff --git a/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
index 9d6dd1a..df61635 100644
--- a/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -372,6 +372,9 @@ public function attachLibrary($library) {
    *
    * @return string|null
    *   The escaped, rendered output, or NULL if there is no valid output.
+   *
+   * @throws \Exception
+   *   When passed $string is an object that has no __toString() method.
    */
   public function escapePlaceholder($env, $string) {
     return '<em class="placeholder">' . $this->escapeFilter($env, $string) . '</em>';
@@ -400,6 +403,9 @@ public function escapePlaceholder($env, $string) {
    * @return string|null
    *   The escaped, rendered output, or NULL if there is no valid output.
    *
+   * @throws \Exception
+   *   When passed $arg is an object that has no __toString() method.
+   *
    * @todo Refactor this to keep it in sync with theme_render_and_autoescape()
    *   in https://www.drupal.org/node/2575065
    */
@@ -431,7 +437,7 @@ public function escapeFilter(\Twig_Environment $env, $arg, $strategy = 'html', $
       elseif (method_exists($arg, '__toString')) {
         $return = (string) $arg;
       }
-      // You can't throw exceptions in the magic PHP __toString methods, see
+      // You can't throw exceptions in the magic PHP __toString() methods, see
       // http://php.net/manual/en/language.oop5.magic.php#object.tostring so
       // we also support a toString method.
       elseif (method_exists($arg, 'toString')) {
@@ -469,7 +475,7 @@ public function escapeFilter(\Twig_Environment $env, $arg, $strategy = 'html', $
   /**
    * Wrapper around render() for twig printed output.
    *
-   * If an object is passed that has no __toString method an exception is thrown;
+   * If an object is passed that has no __toString() method an exception is thrown;
    * other objects are casted to string. However in the case that the object is an
    * instance of a Twig_Markup object it is returned directly to support auto
    * escaping.
@@ -483,6 +489,9 @@ public function escapeFilter(\Twig_Environment $env, $arg, $strategy = 'html', $
    * @return mixed
    *   The rendered output or an Twig_Markup object.
    *
+   * @throws \Exception
+   *   When passed $arg is an object that has no __toString() method.
+   *
    * @see render
    * @see TwigNodeVisitor
    */
@@ -509,7 +518,7 @@ public function renderVar($arg) {
       elseif (method_exists($arg, '__toString')) {
         return (string) $arg;
       }
-      // You can't throw exceptions in the magic PHP __toString methods, see
+      // You can't throw exceptions in the magic PHP __toString() methods, see
       // http://php.net/manual/en/language.oop5.magic.php#object.tostring so
       // we also support a toString method.
       elseif (method_exists($arg, 'toString')) {