diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index fbb7804..e72105b 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -2464,6 +2464,11 @@ function template_process(&$variables, $hook) {
  * @see html.tpl.php
  */
 function template_preprocess_html(&$variables) {
+  // Take over classes on the $page render element.
+  if (isset($variables['page']['#attributes']['class'])) {
+    $variables['classes_array'] = array_merge($variables['classes_array'], $variables['page']['#attributes']['class']);
+  }
+
   // Compile a list of classes that are going to be applied to the body element.
   // This allows advanced theming based on context (home page, node of certain type, etc.).
   // Add a class that tells us whether we're on the front page or not.