--- Makefile.common.orig
+++ Makefile.common
@@ -4,4 +4,4 @@
 CXXWARNFLAGS := -Wall -Wold-style-cast -Wundef -Wsign-compare -Wconversion -Wpointer-arith -pedantic
 CXXFLAGS := $(CXXWARNFLAGS) -g -O2

-prefix := /usr
+prefix := ${PREFIX}