Unknown module(s) in QT: webkit webkitwidgets

I want to install openboard on my Manjaro PC. Here is the problem: if I just get it from AUR, or compile from source, I get

Project ERROR: Unknown module(s) in QT: webkit webkitwidgets

Which is weird: PKGBUILD deps in AUR definately contain webkit:

depends=('qt5-base' 'qt5-multimedia' 'qt5-svg' 'qt5-script' 'qt5-webkit' 'qt5-tools' 'qt5-xmlpatterns' 'libpaper' 'bzip2' 'openssl' 'libfdk-aac' 'sdl' 'ffmpeg')

And when I compile it manually (with simple qmake OpenBoard.pro), I install qt5-webkit package – but it doesn’t help! I guess I’m misunderstanding something about qt5 dependencies and how to satisfy them. What am I doing wrong here?