Can my baby sleep on his tummy?

He’s 3 and a half months but he can easily roll from back to tummy and tummy to back. He recently just started rolling onto his tummy and putting himself to sleep like that. I don’t want to stop him cause he’s doing amazing at self soothing and putting himself to sleep but I don’t want to chance the risk of sids. Is it okay for him to sleep on his tummy or should I just put him on his back?