diff --git a/gtk/gtkstyle.c b/gtk/gtkstyle.c
index 3a44de64a4..b760fea440 100644
--- a/gtk/gtkstyle.c
+++ b/gtk/gtkstyle.c
@@ -1788,6 +1788,8 @@ transform_detail_string (const gchar     *detail,
     gtk_style_context_add_class (context, "menu");
   else if (strcmp (detail, "accellabel") == 0)
     gtk_style_context_add_class (context, "accelerator");
+  else if (strcmp (detail, "menubar") == 0)
+    gtk_style_context_add_class (context, "menubar");
   else if (g_str_has_prefix (detail, "cell"))
     {
       GtkRegionFlags row, col;