TOPIC: Must select one

Hi
I can't see if this is supported.
We setup a drop list with two selects Full Rego / Day Rego
If Day rego is setup then they must select which Day or Days they want, Each day is a check box.
We have enable conditional on the Day Rego for the Days check box fields to be displayed so all good.
But how do we ensure that they select a day as they can't be set to required individually but as a group check boxes we must have one selected.

Solved:
I just included all check boeses into the same field and make it required.