diff --git a/stand/i386/kgzldr/Makefile b/stand/i386/kgzldr/Makefile
index 281f1c9f1ba0..96ba94ee535f 100644
--- a/stand/i386/kgzldr/Makefile
+++ b/stand/i386/kgzldr/Makefile
@@ -7,7 +7,7 @@ STRIP=
 BINMODE=${LIBMODE}
 BINDIR=	${LIBDIR}
 
-SRCS=	start.s boot.c subr_inflate.c lib.c crt.s sio.s
+SRCS=	start.S boot.c subr_inflate.c lib.c crt.S sio.S
 CFLAGS=	-Os
 CFLAGS+=-DKZIP
 NO_SHARED=
@@ -15,6 +15,6 @@ LDFLAGS+=-Wl,-r
 .PATH:	${SYSDIR}/kern
 
 BOOT_COMCONSOLE_PORT?=	0x3f8
-AFLAGS+=--defsym SIO_PRT=${BOOT_COMCONSOLE_PORT}
+ACFLAGS+=-Wa,-defsym,SIO_PRT=${BOOT_COMCONSOLE_PORT}
 
 .include <bsd.prog.mk>
diff --git a/stand/i386/kgzldr/crt.s b/stand/i386/kgzldr/crt.S
similarity index 100%
rename from stand/i386/kgzldr/crt.s
rename to stand/i386/kgzldr/crt.S
diff --git a/stand/i386/kgzldr/sio.s b/stand/i386/kgzldr/sio.S
similarity index 100%
rename from stand/i386/kgzldr/sio.s
rename to stand/i386/kgzldr/sio.S
diff --git a/stand/i386/kgzldr/start.s b/stand/i386/kgzldr/start.S
similarity index 100%
rename from stand/i386/kgzldr/start.s
rename to stand/i386/kgzldr/start.S
diff --git a/stand/i386/mbr/Makefile b/stand/i386/mbr/Makefile
index 26018ffb1378..dca202cb815b 100644
--- a/stand/i386/mbr/Makefile
+++ b/stand/i386/mbr/Makefile
@@ -3,14 +3,14 @@
 PROG=	mbr
 STRIP=
 BINMODE=${NOBINMODE}
-SRCS=	${PROG}.s
+SRCS=	${PROG}.S
 
 # MBR flags: 0x80 -- try packet interface (also known as EDD or LBA)
 BOOT_MBR_FLAGS?=	0x80
 
 ORG=	0x600
 
-AFLAGS+=--defsym FLAGS=${BOOT_MBR_FLAGS}
+ACFLAGS+=-Wa,-defsym,FLAGS=${BOOT_MBR_FLAGS}
 LDFLAGS+=${LDFLAGS_BIN}
 
 .include <bsd.prog.mk>
diff --git a/stand/i386/mbr/mbr.s b/stand/i386/mbr/mbr.S
similarity index 100%
rename from stand/i386/mbr/mbr.s
rename to stand/i386/mbr/mbr.S
diff --git a/stand/i386/pmbr/Makefile b/stand/i386/pmbr/Makefile
index bfd6209f0406..e09bb610fc18 100644
--- a/stand/i386/pmbr/Makefile
+++ b/stand/i386/pmbr/Makefile
@@ -3,11 +3,13 @@
 PROG=	pmbr
 STRIP=
 BINMODE=${NOBINMODE}
-SRCS=	${PROG}.s
+SRCS=	${PROG}.S
+
+BOOT_MBR_FLAGS?=	0
 
 ORG=	0x600
 
-AFLAGS+=--defsym FLAGS=${BOOT_MBR_FLAGS}
+ACFLAGS+=-Wa,-defsym,FLAGS=${BOOT_MBR_FLAGS}
 LDFLAGS+=${LDFLAGS_BIN}
 
 .include <bsd.prog.mk>
diff --git a/stand/i386/pmbr/pmbr.s b/stand/i386/pmbr/pmbr.S
similarity index 100%
rename from stand/i386/pmbr/pmbr.s
rename to stand/i386/pmbr/pmbr.S