diff --git a/usr.sbin/freebsd-update/freebsd-update.sh b/usr.sbin/freebsd-update/freebsd-update.sh
index aa42af13a30..a58b50e9ca2 100644
--- a/usr.sbin/freebsd-update/freebsd-update.sh
+++ b/usr.sbin/freebsd-update/freebsd-update.sh
@@ -755,6 +755,10 @@ fetchupgrade_check_params () {
 	esac
 	chmod 700 ${WORKDIR}
 	cd ${WORKDIR} || exit 1
+	if [ "$BASEDIR" != / ] && [ -z "$UNAME_r" ]; then
+		echo "$(basename $0): -b basedir requires --currently-running to be specified."
+		exit 1
+	fi
 
 	# Generate release number.  The s/SECURITY/RELEASE/ bit exists
 	# to provide an upgrade path for FreeBSD Update 1.x users, since