DB connection problem in production

I have a separate DB for one model in my application and in development
mode the connection is working properly, in production however it isn't.

production:
  adapter: mysql
  host: myhost
  username: root
  password:
  database: production_db

users_production:
  adapter: mysql
  host: myhost
  username: root
  password:
  database: other_db

The model that connects to the other database is called User but the
table it references in other_db is smf_users so my User.rb looks like
this:

class User < ActiveRecord::Base
  establish_connection "users_#{RAILS_ENV}"
  set_table_name "smf_users"
end

In production I'm getting this error:

Mysql::Error: Table 'production_db. smf_users' doesn't exist:

Note how it is trying to connect to the wrong database and so isn't
finding the correct table. As I say, this works in development mode.

Any suggestions?

From the AWDWR book: "If you pass a symbol to establish_connection,
[...]". Maybe you need to convert your string to a symbol?

establish_connection "users_#{RAILS_ENV}".to_sym

Pepe