# cupsfilter: number-up option not working

If I run /usr/sbin/cupsfilter -o number-up=4 -- first.pdf > second.pdf in my Mac's terminal, the file second.pdf is created, but it only has 1 output page per input page. To my knowledge, -o number-up=4 is supposed to create 1 output page for every 4 input pages. How can I achieve this?