is there a better why how can I refactor this code, making sure that values in a Hash are typecasted to true/false if their value is '1' or '0' while leaving unaltered the rest?

I'm using Ruby 2.0.0 if that matters, and I'd like to improve this code.

  def transform
    hsh = {}
    preferences.each do |k, v|
      v = case v
      when '1'
        true
      when '0'
        false
      else
        v
      end
      hsh[k.to_sym] = v
    end
    hsh
  end