diff --git a/sys/boot/defs.mk b/sys/boot/defs.mk
index 4fbc83966dc6..75c354c6254a 100644
--- a/sys/boot/defs.mk
+++ b/sys/boot/defs.mk
@@ -96,6 +96,16 @@ CFLAGS+= -DLOADER_GELI_SUPPORT
 CFLAGS+=	-m32 -mcpu=powerpc
 .endif
 
+# For amd64, there's a bit of mixed bag. Some of the tree (i386, lib*32) is
+# build 32-bit and some 64-bit (lib*, efi). Centralize all the 32-bit magic here
+# and activate it when DO32 is explicitly defined to be 1.
+.if ${MACHINE_ARCH} == "amd64" && ${DO32:U0} == 1
+CFLAGS+=	-m32 -mcpu=i386
+# LD_FLAGS is passed directly to ${LD}, not via ${CC}:
+LD_FLAGS+=	-m elf_i386_fbsd
+AFLAGS+=	--32
+.endif
+
 _ILINKS=machine
 .if ${MACHINE} != ${MACHINE_CPUARCH} && ${MACHINE} != "arm64"
 _ILINKS+=${MACHINE_CPUARCH}
diff --git a/sys/boot/fdt/Makefile b/sys/boot/fdt/Makefile
index 467e424c2baf..a725499d2f78 100644
--- a/sys/boot/fdt/Makefile
+++ b/sys/boot/fdt/Makefile
@@ -22,10 +22,6 @@ CFLAGS+=	-ffreestanding
 CFLAGS+=	-msoft-float
 .endif
 
-.if ${MACHINE_ARCH} == "powerpc64"
-CFLAGS+=	-m32
-.endif
-
 CFLAGS+=	-Wformat -Wall
 
 .include <bsd.stand.mk>
diff --git a/sys/boot/ficl.mk b/sys/boot/ficl.mk
index b6ac8d9096b0..a0a13206b495 100644
--- a/sys/boot/ficl.mk
+++ b/sys/boot/ficl.mk
@@ -14,17 +14,9 @@ FICL_CPUARCH=	${MACHINE_CPUARCH}
 
 .PATH: ${FICLSRC} ${FICLSRC}/${FICL_CPUARCH}
 
-.if ${MACHINE_CPUARCH} == "amd64"
-.if ${DO32:U0} == 1
-CFLAGS+=	-m32 -I.
-.else
+.if ${MACHINE_CPUARCH} == "amd64" && ${DO32:U0} == 0
 CFLAGS+=	-fPIC
 .endif
-.endif
-
-.if ${MACHINE_ARCH} == "powerpc64"
-CFLAGS+=	-m32 -mcpu=powerpc -I.
-.endif
 
 CFLAGS+=	-I${FICLSRC} -I${FICLSRC}/${FICL_CPUARCH} -I${LDRSRC}
 CFLAGS+=	-DBOOT_FORTH
diff --git a/sys/boot/ficl/Makefile b/sys/boot/ficl/Makefile
index 19c2da8eb197..e32e3909687d 100644
--- a/sys/boot/ficl/Makefile
+++ b/sys/boot/ficl/Makefile
@@ -9,13 +9,6 @@ BASE_SRCS=	dict.c ficl.c fileaccess.c float.c loader.c math64.c \
 
 SRCS=		${BASE_SRCS} sysdep.c softcore.c
 CLEANFILES=	softcore.c testmain testmain.o
-.if ${MACHINE_CPUARCH} == "i386" || \
-    (${MACHINE_CPUARCH} == "amd64" && defined(DO32))
-CFLAGS+=	-march=i386
-.endif
-.if ${MACHINE_CPUARCH} == "amd64" && defined(DO32)
-CFLAGS+=	-m32
-.endif
 
 .if defined(HAVE_PNP)
 CFLAGS+=	-DHAVE_PNP
diff --git a/sys/boot/geli/Makefile b/sys/boot/geli/Makefile
index 84ac9bdf6698..b16f7a8c5ab3 100644
--- a/sys/boot/geli/Makefile
+++ b/sys/boot/geli/Makefile
@@ -14,7 +14,7 @@ NO_PIC=
 .if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64"
 CFLAGS+=        -march=i386
 .endif
-.if ${MACHINE_ARCH} == "amd64" || ${MACHINE_ARCH} == "powerpc64"
+.if ${MACHINE_ARCH} == "amd64"
 CFLAGS+=        -m32
 .endif
 
diff --git a/sys/boot/i386/Makefile.inc b/sys/boot/i386/Makefile.inc
index 941a8c49ab9b..b324d1adfef5 100644
--- a/sys/boot/i386/Makefile.inc
+++ b/sys/boot/i386/Makefile.inc
@@ -25,11 +25,6 @@ LDFLAGS_BIN=-e start -Ttext ${ORG} -Wl,-N,-S,--oformat,binary
 LD_FLAGS_BIN=-static -N --gc-sections
 
 .if ${MACHINE_CPUARCH} == "amd64"
-CFLAGS+=	-m32
-ACFLAGS+=	-m32
-# LD_FLAGS is passed directly to ${LD}, not via ${CC}:
-LD_FLAGS+=	-m elf_i386_fbsd
-AFLAGS+=	--32
 DO32=1
 .endif
 
diff --git a/sys/boot/libsa32/Makefile b/sys/boot/libsa32/Makefile
index 862f8868beab..f09811b62128 100644
--- a/sys/boot/libsa32/Makefile
+++ b/sys/boot/libsa32/Makefile
@@ -5,15 +5,9 @@ DO32=1
 .include <bsd.init.mk>
 
 LIB=sa32
-.if ${MACHINE_CPUARCH} == "amd64"
-LIBSA_CPUARCH=i386
-.else
-LIBSA_CPUARCH=${MACHINE_CPUARCH}
-.endif
+LIBSA_CPUARCH=${MACHINE_CPUARCH:C/amd64/i386/}
 
-.if ${MACHINE_ARCH} == "amd64"
-CFLAGS+=	-m32 -I.
-.endif
+CFLAGS+=	-I.
 
 .PATH:	${SASRC}
 .include "${SASRC}/Makefile"
diff --git a/sys/boot/ofw/Makefile.inc b/sys/boot/ofw/Makefile.inc
index e67c0dc904eb..265f86d1ed55 100644
--- a/sys/boot/ofw/Makefile.inc
+++ b/sys/boot/ofw/Makefile.inc
@@ -1,8 +1,3 @@
 # $FreeBSD$
 
-.if ${MACHINE_ARCH} == "powerpc64"
-CFLAGS+=	-m32 -mcpu=powerpc
-LDFLAGS+=	-m elf32ppc_fbsd
-.endif
-
 .include "../Makefile.inc"
diff --git a/sys/boot/uboot/Makefile.inc b/sys/boot/uboot/Makefile.inc
index e67c0dc904eb..265f86d1ed55 100644
--- a/sys/boot/uboot/Makefile.inc
+++ b/sys/boot/uboot/Makefile.inc
@@ -1,8 +1,3 @@
 # $FreeBSD$
 
-.if ${MACHINE_ARCH} == "powerpc64"
-CFLAGS+=	-m32 -mcpu=powerpc
-LDFLAGS+=	-m elf32ppc_fbsd
-.endif
-
 .include "../Makefile.inc"
diff --git a/sys/boot/zfs/Makefile b/sys/boot/zfs/Makefile
index 478e168ef368..7575aa9207eb 100644
--- a/sys/boot/zfs/Makefile
+++ b/sys/boot/zfs/Makefile
@@ -16,14 +16,6 @@ CFLAGS+=	-I${LDRSRC} -I${SYSDIR} -I.
 CFLAGS+=	-I${SYSDIR}/cddl/boot/zfs
 CFLAGS+=	-I${SYSDIR}/crypto/skein
 
-.if ${MACHINE_CPUARCH} == "i386" || \
-	(${MACHINE_CPUARCH} == "amd64" && defined(DO32))
-CFLAGS+=	-march=i386
-.endif
-.if ${MACHINE_CPUARCH} == "amd64" && defined(DO32)
-CFLAGS+=	-m32
-.endif
-
 CFLAGS+=	-Wformat -Wall
 
 .include <bsd.stand.mk>