rolling onto stomach sleeping

My almost 3 month old (next Thursday). Just started rolling into stomach when placed in crib to sleep tonight. I woke up and found him on his stomach, head turned to side, and arm draped through bars hanging down side of crib. Different time I work up and found him face to face with the bars. He's obviously not waking up when he runs into the bars bc he doesn't cry or move enough to wake me. But I'm worried about him hitting his head repeatedly on bars or getting limb stuck.