diff --git a/plugins/systemd/systemd_units b/plugins/systemd/systemd_units
index a8bd3409..5d5f15f4 100755
--- a/plugins/systemd/systemd_units
+++ b/plugins/systemd/systemd_units
@@ -37,7 +37,7 @@ GPLv2
 
 =cut
 
-. $MUNIN_LIBDIR/plugins/plugin.sh
+. "$MUNIN_LIBDIR/plugins/plugin.sh"
 
 states="active \
 	reloading \