diff --git a/usr.sbin/ppp/Makefile b/usr.sbin/ppp/Makefile
index c10dc7f99e0..308df80cf53 100644
--- a/usr.sbin/ppp/Makefile
+++ b/usr.sbin/ppp/Makefile
@@ -23,7 +23,7 @@ CFLAGS+=-DRELEASE_CRUNCH
 .endif
 
 .if defined(PPP_CONFDIR) && !empty(PPP_CONFDIR)
-CFLAGS+=-DPPP_CONFDIR=${PPP_CONFDIR}
+CFLAGS+=-DPPP_CONFDIR=\"${PPP_CONFDIR}\"
 .endif
 
 .if defined(NOKLDLOAD)