Datepicker appears below modal dialog not on the top

Datepicker appears below modal dialog not on the top

Hi, I have modal dialog which contains form, one of the input is date with datepicker binding.

My code is like this:

$("#datum").datepicker({
mandatory: true,
closeText: "zavřít",
dateFormat: "d. m. yy",
monthNames: ['Leden', 'Únor', 'Březen', 'Duben', 'Květen', 'Červen', 'Červenec', 'Srpen', 'Září', 'Říjen', 'Listopad', 'Prosinec'],
dayNamesMin: ['Ne', 'Po', 'Út', 'St', 'Čt', 'Pá', 'So'],
firstDay: 1
});

The problem is that datepicker "window" always shows below the dialog so user can't see it. I have no clue how to bring it into a focus. Playing with z-index didn't help.

Can please somebody help?

Thanks.