SDL2 Fullscreen Mouse

I am currently trying to make a fullscreen option for my game, but when I set it to fullscreen, the mouse doesn’t work as I want.
SDL_GetMouseState gets the current position of the mouse, but when it’s fullscreen the x and y numbers don’t fit to my menu anymore. They just doesn’t scale (while the pictures do).
Is there an easy way to solve that problem, like getting the scaledMouseState?

[I forgot my username :P]