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 550b5ca..b3a75e5 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
@@ -114,3 +114,10 @@ function _test_theme_twig_php_values() {
     ),
   );
 }
+
+/**
+ * Implements template_preprocess_status_messages().
+ */
+function twig_theme_test_preprocess_status_messages(&$variables) {
+  $variables['attributes']['class'][] = 'custom-test-messages-class';
+}
diff --git a/core/modules/system/tests/src/Kernel/Render/ClassyTest.php b/core/modules/system/tests/src/Kernel/Render/ClassyTest.php
new file mode 100644
index 0000000..76cf23e
--- /dev/null
+++ b/core/modules/system/tests/src/Kernel/Render/ClassyTest.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace Drupal\Tests\system\Kernel\Render;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests the Classy theme.
+ *
+ * @group Theme
+ */
+class ClassyTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = array('system', 'twig_theme_test');
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+
+    // Use the classy theme.
+    $this->container->get('theme_installer')->install(['classy']);
+    $this->container->get('config.factory')
+      ->getEditable('system.theme')
+      ->set('default', 'classy')
+      ->save();
+    // Clear the theme registry.
+    $this->container->set('theme.registry', NULL);
+
+  }
+
+  /**
+   * Test the classy theme.
+   */
+  function testClassyTheme() {
+    drupal_set_message('An error occurred', 'error');
+    drupal_set_message('But then something nice happened');
+    $messages = array(
+      '#type' => 'status_messages',
+    );
+    $this->render($messages);
+    $this->assertNoText('custom-test-messages-class', 'The custom class attribute value added in the status messages preprocess function is not displayed as page content.');
+  }
+
+}
diff --git a/core/themes/classy/templates/misc/status-messages.html.twig b/core/themes/classy/templates/misc/status-messages.html.twig
index 683a111..e98964e 100644
--- a/core/themes/classy/templates/misc/status-messages.html.twig
+++ b/core/themes/classy/templates/misc/status-messages.html.twig
@@ -50,7 +50,5 @@
       </div>
     {% endif %}
   </div>
-  {# Remove type specific classes. #}
-  {{ attributes.removeClass(classes) }}
 {% endfor %}
 {% endblock messages %}