Symfony2 environmental variables

I'm trying to use environemntal variables as parameters in Symfony2. However when I run composer update I get:

 [Symfony\Component\DependencyInjection\Exception\ParameterNotFoundException]  
 You have requested a non-existent parameter "compass.bin".

The variables "SYMFONY__COMPASS__BIN" is set both in shell and in apache vhost. Any idea what could cause this?