diff --git a/boot/cdbootblock/Makefile b/boot/cdbootblock/Makefile
index 3dc0ba0d3..c4286b988 100644
--- a/boot/cdbootblock/Makefile
+++ b/boot/cdbootblock/Makefile
@@ -11,7 +11,7 @@ PROG=	cdbootblock
 
 SRCS=		bootblock.s
 .PATH:	${.CURDIR}/../bootblock
-CPPFLAGS+=	-DCDBOOT
+AFLAGS+=	-DCDBOOT
 
 BINDIR=		/usr/mdec
 MAN=