diff --git a/sys/boot/i386/boot0sio/Makefile b/sys/boot/i386/boot0sio/Makefile
index 5b2bad474b30..a6b6ae1cb2f7 100644
--- a/sys/boot/i386/boot0sio/Makefile
+++ b/sys/boot/i386/boot0sio/Makefile
@@ -2,6 +2,7 @@
 
 .PATH: ${.CURDIR}/../boot0
 
-BOOT=	boot0sio
+FILESNAME=	boot0sio
+CFLAGS+=	-DSIO
 
 .include "${.CURDIR}/../boot0/Makefile"