diff --git a/build.sh b/build.sh
index 7cbcd95af138..4a6748bfbeb7 100755
--- a/build.sh
+++ b/build.sh
@@ -1,5 +1,5 @@
 #! /usr/bin/env sh
-#	$NetBSD: build.sh,v 1.203 2009/02/25 23:34:10 lukem Exp $
+#	$NetBSD: build.sh,v 1.204 2009/03/06 16:29:40 apb Exp $
 #
 # Copyright (c) 2001-2009 The NetBSD Foundation, Inc.
 # All rights reserved.
@@ -163,14 +163,23 @@ initdefaults()
 	[ -f share/mk/bsd.own.mk ] ||
 	    bomb "src/share/mk is missing; please re-fetch the source tree"
 
-	# Find information about the build platform.  Note that "uname -p"
-	# is not part of POSIX, but NetBSD's uname -p prints MACHINE_ARCH,
-	# while uname -m prints MACHINE.
+	# Find information about the build platform.  This should be
+	# kept in sync with _HOST_OSNAME, _HOST_OSREL, and _HOST_ARCH
+	# variables in share/mk/bsd.sys.mk.
+	#
+	# Note that "uname -p" is not part of POSIX, but we want uname_p
+	# to be set to the host MACHINE_ARCH, if possible.  On systems
+	# where "uname -p" fails, prints "unknown", or prints a string
+	# that does not look like an identifier, fall back to using the
+	# output from "uname -m" instead.
 	#
 	uname_s=$(uname -s 2>/dev/null)
 	uname_r=$(uname -r 2>/dev/null)
 	uname_m=$(uname -m 2>/dev/null)
-	uname_p=$(uname -p 2>/dev/null || uname -m 2>/dev/null)
+	uname_p=$(uname -p 2>/dev/null || echo "unknown")
+	case "${uname_p}" in
+	''|unknown|*[^a-z0-9]*) uname_p="${uname_m}" ;;
+	esac
 
 	id_u=$(id -u 2>/dev/null || /usr/xpg4/bin/id -u 2>/dev/null)
 
@@ -1204,7 +1213,7 @@ createmakewrapper()
 	eval cat <<EOF ${makewrapout}
 #! ${HOST_SH}
 # Set proper variables to allow easy "make" building of a NetBSD subtree.
-# Generated from:  \$NetBSD: build.sh,v 1.203 2009/02/25 23:34:10 lukem Exp $
+# Generated from:  \$NetBSD: build.sh,v 1.204 2009/03/06 16:29:40 apb Exp $
 # with these arguments: ${_args}
 #
 
diff --git a/share/mk/bsd.own.mk b/share/mk/bsd.own.mk
index fc366ca4c16f..6ac49068afe4 100644
--- a/share/mk/bsd.own.mk
+++ b/share/mk/bsd.own.mk
@@ -1,4 +1,4 @@
-#	$NetBSD: bsd.own.mk,v 1.557 2009/02/25 20:36:45 sketch Exp $
+#	$NetBSD: bsd.own.mk,v 1.558 2009/03/06 16:29:41 apb Exp $
 
 .if !defined(_BSD_OWN_MK_)
 _BSD_OWN_MK_=1
@@ -125,10 +125,16 @@ USETOOLS?=	no
 .if !defined(HOST_OSTYPE)
 _HOST_OSNAME!=	uname -s
 _HOST_OSREL!=	uname -r
-_HOST_ARCH!=	uname -p 2>/dev/null || uname -m
+# For _HOST_ARCH, if uname -p fails, or prints "unknown", or prints
+# something that does not look like an identifier, then use uname -m.
+_HOST_ARCH!=	uname -p 2>/dev/null
+_HOST_ARCH:=	${HOST_ARCH:tW:C/.*[^a-z0-9].*//:S/unknown//}
+.if empty(_HOST_ARCH)
+_HOST_ARCH!=	uname -m
+.endif
 HOST_OSTYPE:=	${_HOST_OSNAME}-${_HOST_OSREL:C/\([^\)]*\)//g:[*]:C/ /_/g}-${_HOST_ARCH:C/\([^\)]*\)//g:[*]:C/ /_/g}
 .MAKEOVERRIDES+= HOST_OSTYPE
-.endif
+.endif # !defined(HOST_OSTYPE)
 
 .if ${USETOOLS} == "yes"						# {