diff --git a/set_shared_user_password.sh b/set_shared_user_password.sh
index acc2c8a660..91ee8d5471 100755
--- a/set_shared_user_password.sh
+++ b/set_shared_user_password.sh
@@ -1,22 +1,35 @@
 #!/bin/bash
 
-# Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+# Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Script to set the password for the shared user account. Stores the MD5crypt'd
 # password to a file inside chroot, for use by build_image.
 
-# This can only run inside the chroot.
-. "$(dirname "$0")/common.sh" || exit 1
+# Make sure common.sh is here.
+SCRIPT_ROOT=$(dirname $(readlink -f "$0"))
+. "${SCRIPT_ROOT}/common.sh" || { echo "Unable to load common.sh"; exit 1; }
+
+assert_inside_chroot
 
 # Die on any errors.
 switch_to_strict_mode
 
 SHARED_USER_PASSWD_FILE="/etc/shared_user_passwd.txt"
 
-# Get password
-read -p "Enter password for shared user account: " PASSWORD
+# If optional password argument is supplied, set password to that.
+if [[ $# > 1 ]]; then
+  echo "Too many arguments."
+  echo "usage: $0 [password]"
+  exit 1
+elif [[ $# == 1 ]]; then
+  PASSWORD=$1
+  exec "$0" < <(echo "$PASSWORD")
+else
+  # Get password
+  read -s -p "Enter password for shared user account: " PASSWORD
+fi
 
 CRYPTED_PASSWD="$(echo "$PASSWORD" | openssl passwd -1 -stdin)"
 PASSWORD="gone now"