SDL doesn't play sound - Annoying problem.

This is the code:
int main()
{
Mix_Music *music = NULL;
music = Mix_LoadMUS("music.ogg");
Mix_PlayMusic(music, 0);
}
It is the simplest program to load a file and play it once.
The Errors are:
Code:
undefined reference to `Mix_LoadMUS'
undefined reference to `Mix_PlayMusic'
ld returned 1 exit status
It is really annoyning because I can't see any errors!