--- ../src-Makefile.orig	2018-12-10 13:17:32.262625152 +0100
+++ ./src/Makefile	2018-12-10 13:17:36.358752414 +0100
@@ -1,4 +1,4 @@
-prefix=/usr
+prefix ?= /usr
 includedir=$(prefix)/include
 libdir=$(prefix)/lib