Rayon parallel iterator is not an iterator?

I'm starting to experiment with the Rayon crate and I'm sure I must be missing something obvious here. If I call par_iter to get one of Rayon's parallel iterators, I can call the usual iterator methods on it (for_each, map, collect...) so it seems to be an iterator. But when I try to use it in a for loop, the compiler insists it is not: error[E0277]: rayon::range::Iter<{integer}> is not an iterator What am I missing here?