diff --git a/stand/i386/loader/Makefile b/stand/i386/loader/Makefile
index 539c736af38f..723220484e67 100644
--- a/stand/i386/loader/Makefile
+++ b/stand/i386/loader/Makefile
@@ -1,123 +1,137 @@
 # $FreeBSD$
 
 HAVE_ZFS=		${MK_LOADER_ZFS}
 
 LOADER_NET_SUPPORT?=	yes
 LOADER_NFS_SUPPORT?=	yes
 LOADER_TFTP_SUPPORT?=	yes
 LOADER_CD9660_SUPPORT?=	yes
 LOADER_EXT2FS_SUPPORT?=	yes
 LOADER_MSDOS_SUPPORT?=	yes
 LOADER_UFS_SUPPORT?=	yes
 LOADER_GZIP_SUPPORT?=	yes
 LOADER_BZIP2_SUPPORT?=	yes
 
 .include <bsd.init.mk>
 
 LOADER?=	loader_${LOADER_INTERP}
 PROG=		${LOADER}.sym
 INTERNALPROG=
 NEWVERSWHAT?=	"bootstrap loader" x86
 VERSION_FILE=	${.CURDIR}/../loader/version
-LOADERSIZE?=	508000		# Largest known safe size for loader.bin
-
+#
+# There's 640k - 40k maximum space, less however much memory the BIOS uses.  A
+# non-random survey suggests that 20k-25k is a good value for 'most' machines.
+# We also need to subtract maximum stack usage (20-25k).
+#
+# So 640k - 40k - 25k - 25k = 550k = 563,200 bytes, but use 550,000 below for
+# some extra buffer for more complex setups and/or wider BIOS lomem variation.
+#
+# Some systems use more stack or have BIOS resere more RAM (or both), and will
+# need to set this lower in /etc/loader.conf if the above buffer is too small.
+#
+# sudo dd if=/dev/mem bs=1 iseek=0x413 count=2 | hd -d
+#
+# will tell you how many kiB of lomem are available.
+#
+LOADERSIZE?=	550000		# Largest known safe size for loader.bin
 
 .PATH:		${BOOTSRC}/i386/loader
 
 # architecture-specific loader code
 SRCS=		main.c conf.c vers.c chain.c gfx_fb.c 8x16.c
 
 CFLAGS.gfx_fb.c += -I${.CURDIR}/../libi386
 CFLAGS.gfx_fb.c += -I$(SRCTOP)/sys/teken
 CFLAGS.gfx_fb.c += -I${SRCTOP}/sys/cddl/contrib/opensolaris/common/lz4
 CFLAGS.gfx_fb.c += -I${SRCTOP}/contrib/pnglite
 CFLAGS.gfx_fb.c += -DHAVE_MEMCPY -I${SRCTOP}/sys/contrib/zlib
 
 # Include bcache code.
 HAVE_BCACHE=	yes
 
 # Enable PnP and ISA-PnP code.
 HAVE_PNP=	yes
 HAVE_ISABUS=	yes
 
 .if ${MK_LOADER_FIREWIRE} == "yes"
 CFLAGS+=	-DLOADER_FIREWIRE_SUPPORT
 LIBFIREWIRE=	${BOOTOBJ}/i386/libfirewire/libfirewire.a
 .endif
 
 .if ${MK_LOADER_ZFS} == "yes"
 CFLAGS.main.c+=	-I${SYSDIR}/contrib/openzfs/include
 CFLAGS.main.c+=	-I${SYSDIR}/contrib/openzfs/include/os/freebsd/zfs
 .endif
 
 .if exists(${.CURDIR}/help.i386)
 HELP_FILES=	${.CURDIR}/help.i386
 .endif
 
 # Always add MI sources
 .include	"${BOOTSRC}/loader.mk"
 
 CLEANFILES+=	${LOADER} ${LOADER}.bin 8x16.c
 
 ORG=		0x0
 
 CFLAGS+=	-Wall
 LDFLAGS+=	-static ${LDFLAGS_ORG} -Wl,--gc-sections
 .if ${LINKER_TYPE} == "lld" && ${LINKER_VERSION} >= 130000
 # lld 13 and higher default to garbage collecting start/stop symbols,
 # completely ruining our linker sets. For now, work around it by
 # disabling this un-feature.
 LDFLAGS+=	-Wl,-z,nostart-stop-gc
 .endif
 
 # i386 standalone support library
 LIBI386=	${BOOTOBJ}/i386/libi386/libi386.a
 CFLAGS+=	-I${BOOTSRC}/i386
 
 # Debug me!
 #CFLAGS+=	-g
 #LDFLAGS+=	-g
 
 8x16.c: ${SRCTOP}/contrib/terminus/ter-u16b.bdf
 	vtfontcvt -f compressed-source -o ${.TARGET} ${.ALLSRC}
 
 
 ${LOADER}: ${LOADER}.bin ${BTXLDR} ${BTXKERN}
 	btxld -v -f aout -e ${LOADER_ADDRESS} -o ${.TARGET} -l ${BTXLDR} \
 		-b ${BTXKERN} ${LOADER}.bin
 
 ${LOADER}.bin: ${LOADER}.sym
 	${STRIPBIN} -R .comment -R .note -o ${.TARGET} ${.ALLSRC}
 	@set -- `ls -l ${.TARGET}` ; x=$$((${LOADERSIZE}-$$5)); \
 	    echo "$$x bytes available"; test $$x -ge 0
 
 .if ${MK_LOADER_ZFS} == "yes" && ${LOADER_INTERP} == ${LOADER_DEFAULT_INTERP}
 LINKS+=		${BINDIR}/${LOADER} ${BINDIR}/zfsloader
 .endif
 .if ${LOADER_INTERP} == ${LOADER_DEFAULT_INTERP}
 LINKS+=		${BINDIR}/${LOADER} ${BINDIR}/loader
 .endif
 FILES+=	${LOADER}
 FILESMODE_${LOADER}= ${BINMODE} -b
 
 # Note: crt0.o needs to be first for pxeboot(8) to work. It assumes that the
 # startup code is located at the start of the loader and will jump
 # there. Although btx is more flexible than this, the emulated boot2 environment
 # that pxeldr provides has none of that flexibility assumes an entry point of
 # 0. In addition, pxeldr and cdboot assume that it is loading an a.out file.
 #
 # We must add it to the LDFLAGS instead of the OBJS because the former won't try
 # to clean it. When it is in OBJS, this cleaning can lead to races where
 # btxcrt.o is rebuilt, but boot2 isn't, leading to errors at installation time.
 # LDFLAGS does not have this baggage and will be included first in the list of
 # files.
 LDFLAGS+=	${BTXCRT}
 
 DPADD=	${LDR_INTERP32} ${LIBFIREWIRE} ${LIBI386} ${LIBSA32}
 LDADD=	${LDR_INTERP32} ${LIBFIREWIRE} ${LIBI386} ${LIBSA32}
 
 .if ${MACHINE_CPUARCH} == "amd64"
 CFLAGS+=	-DLOADER_PREFER_AMD64
 .endif
 
 .include <bsd.prog.mk>