Smooth scroll in Zathura

I am trying to enable the smooth scrolling feature in Zathura. I have the following line in my zathurarc: set smooth-scroll true, but the scrolling doesn't become smooth. According to the documentation: > smooth-scroll > > Defines if scrolling via touchpad should be smooth(only available with gtk >= 3.4). I have gtk 3.22 installed (which is greater than 3.4, right?) as dpkg -s libgtk-3-0|grep '^Version' gives me Version: 3.22.4-1. What do I need to do in order to enable smooth scroll? The "via touchpad" part is also suspicious, but I can't get it to work on either a touchpad, a scrollwheel or with the keyboard. Another suspicious thing is that it does not autocomplete when I type :set sm which it does with other options.