What to do with baby's arms when in grobag

Hi everyone, this seems like a really simple question but what have you done with your baby's arms when putting them in a grobag to sleep? When I've tried, he wakes himself up by moving his arms- swaddling handles that brilliantly. He's showing more interest in walking than rolling so at the moment it's not an issue... But what did you do? Do they just grow out of waking themselves up with their arms flailing?!