Index: Makefile
===================================================================
--- Makefile
+++ Makefile
@@ -307,6 +307,13 @@
 			NXB_TARGET_ARCH=${NXB_TARGET_ARCH}
 .endif
 
+.if ${_TARGET} == "x86_64"
+# Some version of bmake (e.g. Linux and Mac when built with the default flags)
+# will report MACHINE as x86_64
+_TARGET:="amd64"
+_TARGET_ARCH:="amd64"
+.endif
+
 .if make(print-dir)
 .SILENT:
 .endif
Index: Makefile.inc1
===================================================================
--- Makefile.inc1
+++ Makefile.inc1
@@ -447,6 +447,10 @@
 .endif
 .if make(buildworld)
 BUILD_ARCH!=	uname -p
+.if ${BUILD_ARCH} == "x86_64" || (${BUILD_ARCH} == "i386" && ${.MAKE.OS} == "Darwin")
+# Allow crossbuilding from Linux/MacOS where uname -p will print x86_64/i386
+BUILD_ARCH:=amd64
+.endif
 .if ${MACHINE_ARCH} != ${BUILD_ARCH}
 .error To cross-build, set TARGET_ARCH.
 .endif
Index: include/Makefile
===================================================================
--- include/Makefile
+++ include/Makefile
@@ -395,6 +395,10 @@
 # we need MACHINE et al set correctly
 HOST_MACHINE!= uname -m
 HOST_MACHINE_ARCH!= uname -p
+.if ${HOST_MACHINE} == "x86_64"
+HOST_MACHINE:=amd64
+HOST_MACHINE_ARCH:=amd64
+.endif
 MACHINE:= ${HOST_MACHINE}
 MACHINE_ARCH:= ${HOST_MACHINE_ARCH}
 .endif
Index: share/mk/src.sys.env.mk
===================================================================
--- share/mk/src.sys.env.mk
+++ share/mk/src.sys.env.mk
@@ -54,6 +54,13 @@
 .export MAKESYSPATH
 .endif
 
+.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