Undeclared dependency on gio-unix-2.0

I am building GNOME Panel 3.30.0 on NixOS and getting the following error:

clock-applet.c:44:10: fatal error: gio/gdesktopappinfo.h: No such file or directory
 #  include <gio/gdesktopappinfo.h>
            ^~~~~~~~~~~~~~~~~~~
compilation terminated.

Downstream issue: https://github.com/NixOS/nixpkgs/issues/36468, https://github.com/NixOS/nixpkgs/pull/45950#issuecomment-420616594