Villagers won't go up stairs and won't go to sleep

I built a 3-wide, 3-long staircase near a villager's naturally generated house. This is definitely the villager's house, and I've seen him sleeping in it before. However, I found him at night just standing at the bottom of the staircase (his house is at the top). He is a nitwit so I thought I would wait a bit to see if he was just going to bed late, but as the night went on he stayed where he was. I pushed him up the stairs and he immediately ran inside his house, closed the door, and jumped onto his bed but has not actually gotten into it in the few minutes since then. I'm worried that he'll go down the stairs in the day and then get attacked at night by zombies since he doesn't seem to want to go up.