Cannot select checkbox using Capybara

I can't get my test to set a checkbox. Tried all kinds of hints found on Google, but nothing seems to work.

The source for the checkbox is

<div class="ish-field buttons-conditions">
<div class="accept-conditions">
<input tabindex="30"
type="checkbox"
class="ish-input-regular-news"
id="RegisterUserFullEmail_Accepted-1"
value="true"
name="RegisterUserFullEmail_Accepted"

The checkbox is visible on the page. I would expect to be able to simply do: check("RegisterUserFullEmail_Accepted-1") but that doesn't work.

Any suggestions?