diff --git a/gtk/gtkdialog.h b/gtk/gtkdialog.h
index ab1d143..faff3e3 100644
--- a/gtk/gtkdialog.h
+++ b/gtk/gtkdialog.h
@@ -138,7 +138,7 @@ GtkWidget* gtk_dialog_new_with_buttons (const gchar     *title,
                                         GtkWindow       *parent,
                                         GtkDialogFlags   flags,
                                         const gchar     *first_button_text,
-                                        ...);
+                                        ...) G_GNUC_NULL_TERMINATED;
 
 void       gtk_dialog_add_action_widget (GtkDialog   *dialog,
                                          GtkWidget   *child,
