cannot create directory '/factorio/saves': Permission denied

[icheered]

On a fresh docker-compose on my nixos system running docker in rootless mode I get the error in the title.

mkdir my_factorio
sudo chown 845:845 my_factorio
docker-compose up factorio

My docker-compose.yml:

  factorio:
    image: factoriotools/factorio:2.0.21
    container_name: factorio
    ports:
      - "34197:34197/udp"
      - "27015:27015/tcp"
    volumes:
      - ./my_factorio:/factorio
    restart: unless-stopped
    stdin_open: true
    tty: true

I am running NixOS.