Funny... I had the same thing happen to me, but the other way around; I received the non-disc rack when I ordered the disc version. The online company sent me the right one for half price (plus paid for shipping) and I kept the first rack for one of my other bikes. I say keep it; I don't see any harm in using it on a rim-braked bike. Also, you may just buy a disc-braked bike someday and find yourself needing that rack.