--- Makefile.orig	2014-06-29 23:22:47.157452107 +0800
+++ Makefile	2014-06-29 23:23:00.688449516 +0800
@@ -2,7 +2,7 @@
 # $Id: Makefile,v 1.102 2008/03/19 23:05:08 tundra Exp $
 
 install:
-	${BSD_INSTALL_SCRIPT} tbku   ${PREFIX}/bin
-	${BSD_INSTALL_MAN}    tbku.1.gz ${PREFIX}/man/cat1
+	${BSD_INSTALL_SCRIPT} tbku   $(DESTDIR)${PREFIX}/bin
+	${BSD_INSTALL_MAN}    tbku.1.gz $(DESTDIR)${PREFIX}/man/cat1
 
 all:  # Nothing to do here