Starting cron from supervisord.conf

I have a container running debian jessie and I want to run cron. I added this to my supervisord.conf file:

[program:cron]
command = /usr/sbin/cron

But when it container is started cron is not running. I have other things in the supervisord.conf file and they get started, so I know the file is working. And if I manually enter that same command inside the container cron does start, so I know that is installed.

What am I doing wrong or missing?