Ruby On Rails f.checkbox hidden field

I have a check box on a rails form like this:

      .columns.small-1
       = f.label :private
       = f.check_box :private

if the box is unchecked, the form sends correctly with one value passed. If the box is checked the form sends the same field twice with one value as 0 and one as 1, which is causing the box to always show as unchecked" and have a value of 0. Been researching hidden fields in rails but not sure how to apply to this problem.