Extract week from date, start with sunday

Hi,

I am currently extracting my weeks from a date like this..

SELECT INTO extractweek EXTRACT( week FROM ldate );

This works fine, except that this assumes (according
to ISO standard) that weeks starts with Monday.

I need the weeks to start with Sunday instead, otherwise
I will not get the correct week.

Is there a workaround for this?

Thanks!

Kind Regards,
Robert