diff -u -r ../utf8proc-2.1.0/Makefile ./Makefile
--- ../utf8proc-2.1.0/Makefile	2016-12-26 21:52:48.000000000 +0100
+++ ./Makefile	2018-04-17 00:01:15.028065400 +0200
@@ -34,7 +34,7 @@
 endif
 
 # installation directories (for 'make install')
-prefix=/usr/local
+prefix?=/usr/local
 libdir=$(prefix)/lib
 includedir=$(prefix)/include