diff --git a/vpn-daemons/pptp/configure.in b/vpn-daemons/pptp/configure.in
index b6cc9024b1..c18b65224a 100644
--- a/vpn-daemons/pptp/configure.in
+++ b/vpn-daemons/pptp/configure.in
@@ -143,10 +143,15 @@ AS_AC_EXPAND(SBINDIR, $sbindir)
 AS_AC_EXPAND(LIBDIR, $libdir)
 AS_AC_EXPAND(LIBEXECDIR, $libexecdir)
 
-AC_ARG_ENABLE(nm-vpn-dbus-old, [  --enable-nm-vpn-dbus-old  Build Plugin to use old non-'DBUS Dict' NetworkManager VPN interface [default=no]], enable_nm_vpn_dbus_old="$enableval", enable_nm_vpn_dbus_old=no)
+AC_ARG_ENABLE(nm-vpn-dbus-old,
+AC_HELP_STRING([ --enable-nm-vpn-dbus-old], [Build Plugin to use old non-'DBUS Dict' NetworkManager VPN interface [default=no]]), 
+enable_nm_vpn_dbus_old="$enableval", enable_nm_vpn_dbus_old=no)
+NM_VPN_CFLAGS=
 if test "x$enable_nm_vpn_dbus_old" = "xyes" ; then
     NM_VPN_CFLAGS="-DNM_VPN_USE_OLD_DBUS_INTERFACE"
 fi
+AC_SUBST(NM_VPN_CFLAGS)
+
 AC_ARG_ENABLE(bluetooth, [  --enable-bluetooth  Build Bluetooth bits [default=no]], enable_bluetooth="$enableval", enable_bluetooth=no)
 if test "x$enable_bluetooth" = "xyes" ; then
     BUILD_BLUETOOTH="yes"