4 1/4 month old keeps rolling onto his belly while sleeping?

Of course I put him on his back to sleep but within 5 mins he rolls back over to his belly, and the way he rolls in his crib puts his face right in the corner between the bumper and crib matress, pretty scary stuff. So last night after his 4 am feeding I just put him on his belly in the middle of the crib, and he was still there this morning. Is this terrible? It's the only way he wont end up with his face in the corner. I mean I know when we were all babies our moms put us on our bellies to sleep every night, I just really wish he wasn't doing this until 6 months when the risk of SIDS goes down.... And he absolutely wont sleep with the moses blanket or anything that holds him on his back, he can't stand anything to be touching him.