Rolling to belly at night

Hello ladies, my son is 5 months old and started rolling from back to belly a little over a week ago. Tonight when I put him in his crib he was still awake so I left the room, he started crying big cries so I went back to check and he had rolled onto his belly and had his arm through the bars. I picked him up, calmed him down and put him back. He almost immediately rolled over again. This time his arm did not go through the bars but one arm was stuck under his belly. I put him on his back and he did it again. I'm super paranoid now to leave him. I've read that it is safe to let them sleep on their bellies as long as they rolled over on their own, but still... paranoid first time mom over here. Is there anything I can do to keep him from rolling in his sleep? He turned his head so he wasn't face down but now I'm too scared to sleep. I'm sure this is just something I will have to get used to but I didn't know if anyone had any advice!