How do I handle a 404 error from the open method in OpenURI

I was wondering if someone could quickly help me out with how i would
go about handling a 404 error on a page i try and use the open method
on.

begin
  open(some_url)
rescue
  something_went_wrong
end

hrm, i only asked here because i tried that and it didnt work :(. i'll
give it another look maybe something else is amiss.,
Thanks