--- Makefile.orig	2009-11-06 08:23:18.000000000 +0800
+++ Makefile	2009-11-06 08:23:31.000000000 +0800
@@ -25,10 +25,12 @@
 
 # better way to find if we are using ipf or pf
 .if $(OSNAME) == "FreeBSD"
+.if defined(/etc/rc.subr) && defined(/etc/rc.conf)
 FWNAME != . /etc/rc.subr; . /etc/rc.conf; \
           if checkyesno ipfilter_enable; then \
           echo "ipf"; else echo "pf"; fi
 .endif
+.endif
 
 .if $(OSNAME) == "NetBSD"
 FWNAME != . /etc/rc.subr; . /etc/rc.conf; \
