What happens when a couple has twins in China?

I know China has a national policy that each household can have only one child. Each couple that has one kid gets special benefits from the government. I understand families get penalized and have their benefits withdrawn if they have a second child. They don't take the second infant and drop it off a cliff like some ignorant Americans think. I'm aware there are many farming communities that have many children. Meanwhile, I realize accidents and miracles happen. What happens if a couple unexpectedly has a pair of twins? Do they get penalized, too, or does the government allow them to have the benefits?