--- Makefile.orig	2014-06-29 23:52:49.319326073 +0800
+++ Makefile	2014-06-29 23:53:01.269334923 +0800
@@ -4,5 +4,5 @@
 all: # Do nothing.  This is a free-standing Python program.
 
 install:
-	${BSD_INSTALL_SCRIPT} tren.py   ${PREFIX}/bin
-	${BSD_INSTALL_MAN}    tren.1.gz ${PREFIX}/man/man1
+	${BSD_INSTALL_SCRIPT} tren.py   $(DESTDIR)${PREFIX}/bin
+	${BSD_INSTALL_MAN}    tren.1.gz $(DESTDIR)${PREFIX}/man/man1