Index: Makefile
===================================================================
--- Makefile
+++ Makefile
@@ -301,8 +301,8 @@
 .if make(native-xtools*)
 NXB_TARGET:=		${_TARGET}
 NXB_TARGET_ARCH:=	${_TARGET_ARCH}
-_TARGET=		${MACHINE}
-_TARGET_ARCH=		${MACHINE_ARCH}
+_TARGET!=		tools/build/build_machine.sh
+_TARGET_ARCH!=		tools/build/build_machine_arch.sh
 _MAKE+=			NXB_TARGET=${NXB_TARGET} \
 			NXB_TARGET_ARCH=${NXB_TARGET_ARCH}
 .endif
Index: Makefile.inc1
===================================================================
--- Makefile.inc1
+++ Makefile.inc1
@@ -446,7 +446,7 @@
 .error CPUTYPE global should be set with ?=.
 .endif
 .if make(buildworld)
-BUILD_ARCH!=	uname -p
+BUILD_ARCH!=	tools/build/build_machine_arch.sh
 .if ${MACHINE_ARCH} != ${BUILD_ARCH}
 .error To cross-build, set TARGET_ARCH.
 .endif
Index: include/Makefile
===================================================================
--- include/Makefile
+++ include/Makefile
@@ -393,8 +393,8 @@
 .if ${MACHINE} == "host" && !defined(_SKIP_BUILD)
 # we're here because we are building a sysroot...
 # we need MACHINE et al set correctly
-HOST_MACHINE!= uname -m
-HOST_MACHINE_ARCH!= uname -p
-MACHINE:= ${HOST_MACHINE}
-MACHINE_ARCH:= ${HOST_MACHINE_ARCH}
+HOST_MACHINE!=	uname -m
+HOST_MACHINE_ARCH!=	uname -p
+MACHINE!=	${SRCTOP}/tools/build/build_machine.sh
+MACHINE_ARCH!=	${SRCTOP}/tools/build/build_machine_arch.sh
 .endif
Index: share/mk/src.sys.env.mk
===================================================================
--- share/mk/src.sys.env.mk
+++ share/mk/src.sys.env.mk
@@ -54,6 +54,15 @@
 .export MAKESYSPATH
 .endif
 
+# On Linux/MacOS we change MACHINE will be x86_64 by default so we need to
+# change it to amd64 to allow building on those systems.
+.if ${MACHINE} == "x86_64"
+MACHINE:=amd64
+MACHINE_ARCH:=amd64
+.export MACHINE
+.export MACHINE_ARCH
+.endif
+
 .if ${RELDIR:U} == "." && ${.MAKE.LEVEL} == 0
 .sinclude "${.CURDIR}/Makefile.sys.inc"
 .endif
Index: tools/build/build_machine.sh
===================================================================
--- /dev/null
+++ tools/build/build_machine.sh
@@ -0,0 +1,10 @@
+#!/bin/sh -e
+
+build_arch=$(uname -p)
+if [ "${build_arch}" = "x86_64" ]; then
+	build_arch="amd64"
+elif [ "${build_arch}" = "i386" ] && [ "$(uname -m)" = "x86_64" ]; then
+	# On MacOS uname -m reports i386 even on 64bit systems
+	build_arch="amd64"
+fi
+echo "${build_arch}"
Index: tools/build/build_machine_arch.sh
===================================================================
--- /dev/null
+++ tools/build/build_machine_arch.sh
@@ -0,0 +1,7 @@
+#!/bin/sh -e
+
+build_machine=$(uname -m)
+if [ "${build_machine}" = "x86_64" ]; then
+	build_machine="amd64"
+fi
+echo "${build_machine}"