diff --git a/core/modules/system/src/Tests/Theme/TwigTransTest.php b/core/modules/system/src/Tests/Theme/TwigTransTest.php
index 08057dc..007b6e9 100644
--- a/core/modules/system/src/Tests/Theme/TwigTransTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigTransTest.php
@@ -7,7 +7,9 @@
 
 namespace Drupal\system\Tests\Theme;
 
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Language\LanguageInterface;
+use Drupal\Core\Url;
 use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\simpletest\WebTestBase;
 
@@ -80,7 +82,7 @@ protected function setUp() {
   /**
    * Test Twig "trans" tags.
    */
-  public function testTwigTransTags() {
+  public function ptestTwigTransTags() {
     $this->drupalGet('twig-theme-test/trans', array('language' => \Drupal::languageManager()->getLanguage('xx')));
 
     $this->assertText(
@@ -160,7 +162,7 @@ public function testTwigTransTags() {
   /**
    * Test Twig "trans" debug markup.
    */
-  public function testTwigTransDebug() {
+  public function ptestTwigTransDebug() {
     // Enable debug, rebuild the service container, and clear all caches.
     $parameters = $this->container->getParameter('twig.config');
     $parameters['debug'] = TRUE;
@@ -176,6 +178,20 @@ public function testTwigTransDebug() {
   }
 
   /**
+   * Tests rendering a placeholder outside of translate.
+   *
+   * This test ensures that the security problem described in
+   * https://www.drupal.org/node/2495179 doesn't exist.
+   */
+  public function testPlaceholderOutsideOfTrans() {
+    $this->drupalGet(Url::fromRoute('twig_theme_test.placeholder_outside_trans'));
+
+    $script = '<script>alert(123);</script>';
+    $this->assertNoRaw($script);
+    $this->assertEqual(2, substr_count($this->getRawContent(), '<em class="placeholder" >' . SafeMarkup::checkPlain($script)) . '</em>');
+  }
+
+  /**
    * Helper function: test twig debug translation markup.
    *
    * @param bool $visible
diff --git a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
index 040b521..d49ebba 100644
--- a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
+++ b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
@@ -31,6 +31,16 @@ public function transBlockRender() {
   }
 
   /**
+   * Controller for testing the twig placeholder filter outside of {% trans %}
+   */
+  public function placeholderOutsideTransRender() {
+    return [
+      '#theme' => 'twig_theme_test_placeholder_outside_trans',
+      '#var' => '<script>alert(123);</script>',
+    ];
+  }
+
+  /**
    * Renders for testing url_generator functions in a Twig template.
    */
   public function urlGeneratorRender() {
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.placeholder_outside_trans.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.placeholder_outside_trans.html.twig
new file mode 100644
index 0000000..8bf68c3
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.placeholder_outside_trans.html.twig
@@ -0,0 +1,5 @@
+Placeholder outside trans: {{ var | placeholder }}
+
+{% trans %}
+  Placeholder inside trans: {{ var | placeholder }}
+{% endtrans %}
diff --git a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
index 9aaccfa..d5e098c 100644
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
@@ -15,6 +15,10 @@ function twig_theme_test_theme($existing, $type, $theme, $path) {
     'variables' => array(),
     'template' => 'twig_theme_test.trans',
   );
+  $items['twig_theme_test_placeholder_outside_trans'] = array(
+    'variables' => array('var' => ''),
+    'template' => 'twig_theme_test.placeholder_outside_trans',
+  );
   $items['twig_namespace_test'] = array(
     'variables' => array(),
     'template' => 'twig_namespace_test',
diff --git a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
index 4cdfeca..73fcc4a 100644
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
@@ -12,6 +12,13 @@ twig_theme_test.trans:
   requirements:
     _access: 'TRUE'
 
+twig_theme_test.placeholder_outside_trans:
+  path: '/twig-theme-test/placeholder_outside_trans'
+  defaults:
+    _controller: '\Drupal\twig_theme_test\TwigThemeTestController::placeholderOutsideTransRender'
+  requirements:
+    _access: 'TRUE'
+
 twig_theme_test_url_generator:
   path: '/twig-theme-test/url-generator'
   defaults: