Index: usr.sbin/freebsd-update/freebsd-update.sh
===================================================================
--- usr.sbin/freebsd-update/freebsd-update.sh
+++ usr.sbin/freebsd-update/freebsd-update.sh
@@ -686,6 +686,19 @@
 			;;
 	esac
 
+	case ${ARCH} in
+		i386 | amd64)
+			;;
+		*)
+			echo -n "`basename $0:`"
+			cat <<- EOF
+				Upgrading from '${ARCH}' is unsupported by `basename $0`.
+				Instead, FreeBSD can be directly upgraded by source.
+			EOF
+			exit 1
+			;;
+	esac
+
 	# Figure out what directory contains the running kernel
 	BOOTFILE=`sysctl -n kern.bootfile`
 	KERNELDIR=${BOOTFILE%/kernel}