diff --git a/app_win_2_back.hpp b/app_win_2_back.hpp
index f7693c6..fdb5d21 100644
--- a/app_win_2_back.hpp
+++ b/app_win_2_back.hpp
@@ -9,11 +9,11 @@ namespace learn_gtkmm4 {
 }
 
 namespace Gtk {
+    class Builder;
     class Switch;
 }
 
 namespace gui_to_app {
-
     class AppWin2Back final : public Gtk::Application {
     public:
         ~AppWin2Back() noexcept final = default;
@@ -30,6 +30,7 @@ namespace gui_to_app {
     private:
         void on_quit() noexcept;
 
+        Glib::RefPtr<Gtk::Builder> app_builder;
         learn_gtkmm4::HelloWorld *main_window{ nullptr };
         Gtk::Switch *sword_switch{ nullptr };
         Gtk::Switch *lance_switch{ nullptr };
@@ -46,7 +47,6 @@ namespace gui_to_app {
         Gtk::Switch *rock_kit_switch{ nullptr };
         Gtk::Switch *sack_switch{ nullptr };
     };
-
 } // gui_to_app
 
 #endif //LEARNGTK4_APP_WIN_2_BACK_HPP