diff --git a/src/Magnum/Platform/Sdl2Application.cpp b/src/Magnum/Platform/Sdl2Application.cpp
index 276c7ee55..fa65147de 100644
--- a/src/Magnum/Platform/Sdl2Application.cpp
+++ b/src/Magnum/Platform/Sdl2Application.cpp
@@ -812,6 +812,12 @@ void Sdl2Application::exit(const int exitCode) {
 }
 
 bool Sdl2Application::mainLoopIteration() {
+    #ifndef CORRADE_TARGET_EMSCRIPTEN
+    CORRADE_ASSERT(_window, "Platform::Sdl2Application::mainLoopIteration(): no window opened", {});
+    #else
+    CORRADE_ASSERT(_surface, "Platform::Sdl2Application::mainLoopIteration(): no window opened", {});
+    #endif
+
     #ifndef CORRADE_TARGET_EMSCRIPTEN
     const UnsignedInt timeBefore = _minimalLoopPeriod ? SDL_GetTicks() : 0;
     #endif