diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index bd50008..bcfb977 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -269,7 +269,7 @@ function _drupal_theme_initialize($theme, $base_theme = array(), $registry_callb
   // @todo Make twig the default engine and remove this. This is required
   // because (by design) the theme system doesn't allow modules to register more
   // than one type of extension. We need a temporary backwards compatibility
-  // layer to allow us to perform core-wide .tpl.php to .twig conversion.
+  // layer to allow us to perform core-wide .tpl.php to .html.twig conversion.
   include_once DRUPAL_ROOT . '/core/themes/engines/twig/twig.engine';
 
   if (isset($registry_callback)) {
diff --git a/core/modules/node/templates/node.html.twig b/core/modules/node/templates/node.html.twig
index 2d4a674..f1e0b5a 100644
--- a/core/modules/node/templates/node.html.twig
+++ b/core/modules/node/templates/node.html.twig
@@ -9,7 +9,7 @@
  *   or print a subset such as {{ content.field_example }}. Use
  *   {% hide(content.field_example) %} to temporarily suppress the printing
  *   of a given element.
- * - user_picture: The node author's picture from user-picture.twig.
+ * - user_picture: The node author's picture from user-picture.html.twig.
  * - date: Formatted creation date. Preprocess functions can reformat it by
  *   calling format_date() with the desired parameters on
  *   $variables['created'].
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
index 0316fcc..13b649c 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
@@ -58,7 +58,7 @@ function testFindThemeTemplates() {
     // Check for correct content
     // @todo Remove this tests once double engine code is removed
 
-    $this->assertEqual($cache['node']['template_file'], 'core/modules/node/templates/node.twig', 'Node is using node.twig as template file');
+    $this->assertEqual($cache['node']['template_file'], 'core/modules/node/templates/node.html.twig', 'Node is using node.html.twig as template file');
     $this->assertEqual($cache['node']['engine'], 'twig', 'Node is using twig engine');
 
     $this->assertEqual($cache['theme_test_template_test']['template_file'], 'core/modules/system/tests/modules/theme_test/templates/theme_test.template_test.tpl.php', 'theme_test is using theme_test.template_test.tpl.php as template file');
diff --git a/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.html.twig b/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.html.twig
new file mode 100644
index 0000000..6cda319
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.html.twig
@@ -0,0 +1,2 @@
+{# Output for Theme API test #}
+Success: Template overridden.
diff --git a/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.twig b/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.twig
deleted file mode 100644
index 6cda319..0000000
--- a/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.twig
+++ /dev/null
@@ -1,2 +0,0 @@
-{# Output for Theme API test #}
-Success: Template overridden.