How to marshal a byte/uint8 array as json array in Go?

I've got a struct with a []uint8 member and I'm writing it with json.Marshal. Trouble is, it's interpreting the uint8s as chars and it outputs a string rather than an array of numbers.

I can get this to work if it's a []int, but I don't want to have to allocate and copy over the items if I can avoid it. Can I?