Always look for includes in $(PREFIX)/include

src/Makefile

@@ -3,8 +3,8 @@ PREFIX	= /usr/local
 DESTDIR	= 
 LIBDIR	= $(PREFIX)/lib
 CC	= cc
-CPPFLAGSF=
-CPPFLAGS= -I ../include
+CPPFLAGSF= -I $(PREFIX)/include -I ../include
+CPPFLAGS=
 CFLAGSF	= -W
 CFLAGS	= -Wall -g -O2 -pedantic
 AR	= ar -rc

src/project.conf

@@ -1,5 +1,5 @@
 targets=libcpp,cpp
-cppflags=-I ../include
+cppflags_force=-I $(PREFIX)/include -I ../include
 cflags_force=-W
 cflags=-Wall -g -O2 -pedantic
 dist=Makefile,common.h,parser.h