Ruby Date.strptime doesn't enforce 4-digit year

I would expect this code to give me an `ArgumentError: invalid date` error. In Ruby 2.0.0 irb: ``` irb(main):003:0> Date.strptime('05-10-2014', '%Y-%m-%d') => #<Date: 0005-10-20 ((1723177j,0s,0n),+0s,2299161j)> ``` Am I doing something wrong or will Ruby accept a 2-digit year even when I specify `%Y`? I am looking at testing user input. In this case my program is expecting it in the `%Y-%m-%d` and the input date was "entered" in the wrong format, but `strptime` says it's ok.