freebsd 6.1 make问题

打算在freebsd6.1 安装snmp,但make时出错 Makefile:20: *** missing separator. Stop.

具体如下
cd /usr/ports/net-mgmt/net-snmp
make
出现错误信息
Makefile:20: *** missing separator. Stop

makefile 的第20行内容为
13 MASTER_SITE_SUBDIR= net-snmp
14 PKGNAMEPREFIX= net-
15 DISTNAME= ${PKGNAMEPREFIX}${PORTNAME}-${PORTVERSION}
16
17 MAINTAINER= [email protected]
18 COMMENT= An extendable SNMP implementation
19
20 .if !defined(WITH_TKMIB)
21 EXTRA_PATCHES+= ${PATCHDIR}/extra-patch-local:Makefile.in
22 .endif
23
24 .if defined(WITH_TKMIB)
25 RUN_DEPEND= ${SITE_PERL}/${PERL_ARCH}/Tk.pm{PORTSDIR}/x11-toolkits/p5-Tk
26 .endif
27 PATCH_DEPENDS= ${LIBTOOL_DEPENDS}

高手来帮助解决一下

ps
网上查了一下说加什么tab，不起作用