--- Makefile.orig	2018-11-24 02:18:17 UTC
+++ Makefile
@@ -3,11 +3,11 @@
 # Please read the next few lines and enter the correct values.
 
 # where to install GRPN
-PREFIX = /usr/local
-MANDIR = ${PREFIX}/man
+PREFIX ?= /usr/local
+MANDIR ?= ${MANPREFIX}/man
 
 # What compiler should be used
-CC = gcc 
+CC ?= gcc
 
 # NOTE:
 #
@@ -16,10 +16,8 @@ CC = gcc 
 # add -DUSE_GNOME if you want to make grpn GNOME compliant.
 
 
-CFLAGS = -Wall -g -O2 -I/usr/X11/include -DUSE_PANGO `pkg-config --cflags gtk+-2.0` -DGTK_VER_1_1
+CFLAGS += -Wall -DUSE_PANGO `pkg-config --cflags gtk+-2.0` -DGTK_VER_1_1
 
-DFLAGS =  -L/usr/X11/lib 
-
 # end of user configurable section
 
 
@@ -32,6 +30,8 @@ OBJS = test_gtk_ver.o real.o complex.o matrix.o number
 	error.o help.o mode.o undo.o
 
 LIBS   = `pkg-config --libs gtk+-2.0` -lX11 -lm
+
+all: grpn
 
 grpn:	$(OBJS)
 	$(CC) $(DFLAGS) -o $@ $(OBJS) $(LIBS)