I think it's a little more nebulous than that.   I think most allocators are aligned on a boundary, but I don't think it's guaranteed.  Basically, any return from malloc is guaranteed to be aligned for the storage of any standard type object.  So, we're assuming there will be a standard type on every system that will require even-byte alignment, which should be safe, but it's not guaranteed by any standard of which I'm aware.   I'll add more wording to the comment to clarify that, let me know if that's incorrect.