--- ./common.mak	2015-12-31 19:42:10.000000000 +0000
+++ ../common.mak	2018-01-11 19:43:11.319604821 +0000
@@ -207,7 +207,7 @@
 
 CFLAGS          += $(OPTFLAGS) $(REVFLAGS) $(COMMON_CFLAGS)
 
-prefix          = /usr/local
+prefix          ?= /usr/local
 bindir          = $(prefix)/bin
 sbindir         = $(prefix)/sbin
 mandir          = $(prefix)/share/man/man1