Index: head/lib/libstand/Makefile
===================================================================
--- head/lib/libstand/Makefile
+++ head/lib/libstand/Makefile
@@ -28,7 +28,7 @@
 CFLAGS.gcc+=	-mpreferred-stack-boundary=2
 .endif
 .if ${MACHINE_CPUARCH} == "amd64"
-CFLAGS+=	-fPIC
+CFLAGS+=	-fPIC -mno-red-zone
 .endif
 .if ${MACHINE} == "pc98"
 CFLAGS+=	-Os
Index: head/sys/boot/amd64/Makefile.inc
===================================================================
--- head/sys/boot/amd64/Makefile.inc
+++ head/sys/boot/amd64/Makefile.inc
@@ -5,7 +5,7 @@
 BINDIR?=	/boot
 
 # See conf/kern.mk for the correct set of these
-CFLAGS+=	-ffreestanding
+CFLAGS+=	-ffreestanding -mno-red-zone
 CFLAGS+=	-mno-mmx -mno-sse -mno-aes -mno-avx -msoft-float
 LDFLAGS+=	-nostdlib
 
Index: head/sys/boot/efi/libefi/Makefile
===================================================================
--- head/sys/boot/efi/libefi/Makefile
+++ head/sys/boot/efi/libefi/Makefile
@@ -9,7 +9,7 @@
 SRCS+= nullconsole.c comconsole.c
 
 .if ${MACHINE_ARCH} == "amd64"
-CFLAGS+= -fPIC
+CFLAGS+= -fPIC -mno-red-zone
 .endif
 CFLAGS+= -I${.CURDIR}/../include
 CFLAGS+= -I${.CURDIR}/../include/${MACHINE_CPUARCH}
Index: head/sys/boot/ficl/Makefile
===================================================================
--- head/sys/boot/ficl/Makefile
+++ head/sys/boot/ficl/Makefile
@@ -21,6 +21,9 @@
 CFLAGS+=	-march=i386
 CFLAGS.gcc+=	-mpreferred-stack-boundary=2
 .endif
+.if ${MACHINE_CPUARCH} == "amd64"
+CFLAGS+=	-mno-red-zone
+.endif
 .if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64"
 CFLAGS+=	-mno-mmx -mno-3dnow -mno-sse -mno-sse2 -mno-sse3 -msoft-float
 .endif