How to use char instead of varchar when generating db tables from entities?

I'm using string(32) instead of integer for entity id field (it simulates guid type). But after creating database table from entity ids field type is set to varchar(32). I think it's not the best idea, guid always has length = 32 so char type will be more appropriate.

Is there a way to tell Doctrine to use char or the only way is to change it manually in database?