diff --git a/make/rules.in b/make/rules.in
index 60a8f75c65..62a3c4b208 100644
--- a/make/rules.in
+++ b/make/rules.in
@@ -85,6 +85,8 @@ install clean distclean::
 ###	CINCLUDES
 ###	CDEFINES
 ###	CWARNINGS
+### User may define externally
+###     EXT_CFLAGS
 
 CC = 		@CC@
 CFLAGS =	@CFLAGS@
@@ -103,7 +105,7 @@ ALL_CPPFLAGS = \
 	${ALWAYS_INCLUDES} ${CINCLUDES} ${STD_CINCLUDES} \
 	${ALWAYS_DEFINES} ${CDEFINES} ${STD_CDEFINES}
 
-ALL_CFLAGS = ${CFLAGS} \
+ALL_CFLAGS = ${EXT_CFLAGS} ${CFLAGS} \
 	${ALL_CPPFLAGS} \
 	${ALWAYS_WARNINGS} ${STD_CWARNINGS} ${CWARNINGS}