-substs.set('PACKAGE_URL', 'https://www.freedesktop.org/wiki/Software/systemd')
-substs.set('PACKAGE_VERSION', meson.project_version())
+substs.set('PROJECT_URL', 'https://www.freedesktop.org/wiki/Software/systemd')
+substs.set('PROJECT_VERSION', meson.project_version())
+
+# This is to be used instead of meson.source_root(), as the latter will return
+# the wrong result when systemd is being built as a meson subproject
+project_source_root = meson.current_source_dir()