$or works differently than I expected

[Misophistful]

I've just started playing with loco, but I've hit an immediate brick wall where $or isn't behaving how I expected it to.

I'm trying to solve Project Euler problem 1, which is nice and easy with the for macro:

(for [x (range 1 10)
      :when (or (= 0 (mod x 3))
                (= 0 (mod x 5)))]
  x)

=> (3 5 6 9)

But my first attempt at a similar approach with loco didn't work:

(solutions
  [($in :x 1 9)
   ($or ($= 0 ($mod :x 3))
        ($= 0 ($mod :x 5)))])

=> ({:x 1} {:x 2} {:x 3} {:x 4} {:x 5} {:x 6} {:x 7} {:x 8} {:x 9})

I'm guessing that I've totally misunderstood how $or should be used, so I'd really appreciate a prod in the right direction.

Thanks for your work on this cool project.

Cheers, James