4 month good head control but can't roll.

Karine 🌷 • Mom of two handsome boys.💙 English is not my native language! Please excuse any mistakes.✌🏻

My baby is 4 months old and really have a great head control and when laying on his back he can roll on his side, but not on his tummy. And when on his tummy he can't roll on his back yet. Is he supposed to have reach this milestone yet!? He done it only one time.