Index: libnatpmp-20140401/Makefile
===================================================================
--- libnatpmp-20140401.orig/Makefile
+++ libnatpmp-20140401/Makefile
@@ -25,10 +25,10 @@ APIVERSION = 1
 #LDFLAGS = -Wl,--no-undefined
 CFLAGS ?= -Os
 #CFLAGS = -g -O0
-CFLAGS += -fPIC
-CFLAGS += -Wall
+override CFLAGS += -fPIC
+override CFLAGS += -Wall
 #CFLAGS += -Wextra
-CFLAGS += -DENABLE_STRNATPMPERR
+override CFLAGS += -DENABLE_STRNATPMPERR
 #CFLAGS += -Wstrict-aliasing
 
 LIBOBJS = natpmp.o getgateway.o