3 month old tummy sleeping?

Melissa • Baby Bruce 6-3-19💙🌈

My son is able to roll tummy to back & back to tummy. I put him to sleep on his back, but when I got him out of his crib he was on his tummy sleeping. I know tummy sleeping isn’t recommended until age 1 or older. How can I stop him from sleeping on his tummy or is he okay being that he can roll?