Cron Schedule for 1st sunday of the month?

[tonkajeep34]

I'm working on a backup script and i've got it working perfectly in cron. However is it possible to schedule cron to only run the first Sunday of the month?

I thought maybe this would work, but i think that's going to run the 1-7th AND Sunday. What i was trying for is Sun day if it's the 1st through 7th.

0 0 1-7 * sun command

Thanks