diff --git a/docs/reference/gtk/gtk3-sections.txt b/docs/reference/gtk/gtk3-sections.txt
index e37a61fb63..754eb8a185 100644
--- a/docs/reference/gtk/gtk3-sections.txt
+++ b/docs/reference/gtk/gtk3-sections.txt
@@ -5998,6 +5998,7 @@ GTK_STYLE_CLASS_NEEDS_ATTENTION
 GTK_STYLE_CLASS_NOTEBOOK
 GTK_STYLE_CLASS_OSD
 GTK_STYLE_CLASS_PANE_SEPARATOR
+GTK_STYLE_CLASS_POPUP
 GTK_STYLE_CLASS_PRIMARY_TOOLBAR
 GTK_STYLE_CLASS_PROGRESSBAR
 GTK_STYLE_CLASS_PULSE
diff --git a/gtk/gtkmenu.c b/gtk/gtkmenu.c
index 7c137272aa..4dac40c85e 100644
--- a/gtk/gtkmenu.c
+++ b/gtk/gtkmenu.c
@@ -1100,7 +1100,8 @@ gtk_menu_init (GtkMenu *menu)
   gtk_window_set_mnemonic_modifier (GTK_WINDOW (priv->toplevel), 0);
 
   _gtk_window_request_csd (GTK_WINDOW (priv->toplevel));
-  gtk_style_context_add_class (gtk_widget_get_style_context (priv->toplevel), "popup");
+  gtk_style_context_add_class (gtk_widget_get_style_context (priv->toplevel),
+                               GTK_STYLE_CLASS_POPUP);
 
   /* Refloat the menu, so that reference counting for the menu isn't
    * affected by it being a child of the toplevel
diff --git a/gtk/gtkstylecontext.h b/gtk/gtkstylecontext.h
index 8a8351c455..41607f50ac 100644
--- a/gtk/gtkstylecontext.h
+++ b/gtk/gtkstylecontext.h
@@ -798,6 +798,15 @@ struct _GtkStyleContextClass
 
 /* Predefined set of widget regions */
 
+/**
+ * GTK_STYLE_CLASS_POPUP:
+ *
+ * A CSS class that is added to the toplevel windows used for menus.
+ *
+ * Since: 3.14
+ */
+#define GTK_STYLE_CLASS_POPUP "popup"
+
 /**
  * GTK_STYLE_REGION_ROW:
  *