Make a local Symfony 2.8 app act like it's in a prod environment

I have an application based on Symfony 2.8. A feature is working well in my local dev environment but failing in production. I want to make my local environment use prod mode in order to hopefully replicate the problem. What I have tried:

export SYMFONY_ENV=prod
app/console cache:clear --no-warmup

This appeared at first to be working, as I got a message about the cache being cleared in the prod environment, but when I loaded the app, the debug toolbar was visible and said I was in dev mode.

I have also tried looking in both parameters.yml and config.yml for any denotation of the environment. I didn't find anything.

What should I try next?