diff --git a/src/Application/Application.h b/src/Application/Application.h
index 9c16709..1a18a16 100644
--- a/src/Application/Application.h
+++ b/src/Application/Application.h
@@ -186,6 +186,7 @@ class Application: public Platform::Sdl2Application, public efsw::FileWatchListe
 
         template<typename Functor, typename... Args>
         bool drawUnsafeWidget(Functor func, Args... args) {
+            static_assert(std::is_invocable_r_v<bool, Functor, Args...>);
             GameState game_state = _gameState; // Copying the value to reduce the risk of a data race.
             ImGui::BeginDisabled(game_state != GameState::NotRunning);
             bool result = func(std::forward<Args>(args)...);