diff --git a/core/modules/forum/forum.module b/core/modules/forum/forum.module
index 49fdd35..a7f8bc0 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -94,6 +94,7 @@ function forum_theme() {
     ),
     'forum_form' => array(
       'render element' => 'form',
+      'template' => 'forum-form',
     ),
   );
 }
@@ -852,19 +853,3 @@ function template_preprocess_forum_submitted(&$variables) {
   }
   $variables['time'] = isset($variables['topic']->created) ? format_interval(REQUEST_TIME - $variables['topic']->created) : '';
 }
-
-/**
- * Returns HTML for a forum form.
- *
- * By default this does not alter the appearance of a form at all, but is
- * provided as a convenience for themers.
- *
- * @param $variables
- *   An associative array containing:
- *   - form: A render element representing the form.
- *
- * @ingroup themeable
- */
-function theme_forum_form(array $variables) {
-  return drupal_render_children($variables['form']);
-}
diff --git a/core/modules/forum/templates/forum-form.html.twig b/core/modules/forum/templates/forum-form.html.twig
new file mode 100644
index 0000000..56fa0c6
--- /dev/null
+++ b/core/modules/forum/templates/forum-form.html.twig
@@ -0,0 +1,13 @@
+{#
+/**
+ * @see
+ * Default theme implementation for a forum form.
+ *
+ * Available variables:
+ * - form: The complete form. Use 'form' to print the entire form, or print a
+ *   subset such as 'form.title'.
+ *
+ * @ingroup themeable
+ */
+#}
+{{ form }}