Method doesn't compile when defined in a mixin, but is fine without?

[pineapple via Digitalmars-d-learn]

Strangely, though I'm getting this error when wrapping 
SDL_GetWindowMinimumSize and SDL_GetWindowMaximumSize, I don't 
get any compilation errors wrapping the identically-signatured 
SDL_GetWindowSize and SDL_GetWindowPosition using the same mixin.