Larian Studios Forums Divinity - Original Sin Divinity - Original Sin - General Why does my attack vary between 3 and 4 AP?

I've been using a one-handed sword and my attacks are supposed to take 3 AP, but sometimes it takes 4. My character isn't moving before the attack. He'll start his turn and the enemy positions haven't changed from the previous round and the action point cost will suddenly change. What's going on here?