How to select date from a select box using Capybara in Rails 3?

I'm writing a spec for a controller in Rails 3 project using RSpec and Capybara, and I want to select current date from a select box. I tried:

select Date.today, :from => 'Date of birth'

but the spec fails and I get error:

Failure/Error: select Date.today, :from => 'Date of birth' NoMethodError: undefined method `to_xpath' for Mon, 18 Jul 2011:Date

How to fix it?

P.S. In view file I use simple_form_for tag and the select box is generated by code:

f.input :date_of_birth