--- palo/Makefile
+++ palo/Makefile
@@ -11,10 +11,11 @@
 
 OS := $(shell uname -s)
 CC=gcc
+
+CFLAGS ?= -g -O
+CFLAGS += -I../include -I../lib
 ifeq ($(strip ${OS}),HP-UX)
-CFLAGS=-g -O -I../include -I../lib -I$(PA)/include
-else
-CFLAGS=-g -O -I../include -I../lib
+CFLAGS += -I$(PA)/include
 endif
 
 # LDFLAGS=-Wl,-Bstatic 
--- ipl/Makefile
+++ ipl/Makefile
@@ -21,7 +21,8 @@
 # Source sharing with palo
 VPATH=../lib:.
 
-CFLAGS	= -I. -I../lib -I../include -O2 -mdisable-fpregs -Wall
+CFLAGS ?= -O2
+CFLAGS += -I. -I../lib -I../include -mdisable-fpregs -Wall
 LDFLAGS  = -N --section-start .init=0x60000 -e '$$START$$'
 
 all:	iplelf