Rails 3 migrations: Adding reference column?

If I create a new rails 3 migration with (for example) rails g migration tester title:tester user:references , everything works fine...however if I add a column with something along the lines of: rails g migration add_user_to_tester user:references the reference field is not recognised. In short, the question is: how do I add a referencing column to a rails migration from the command line?