diff --git a/tempest/config.py b/tempest/config.py
index b867980..3d3ddff 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -1048,7 +1048,7 @@
     # TODO(yfried): add support for dhcpcd
     cfg.StrOpt('dhcp_client',
                default='udhcpc',
-               choices=["udhcpc", "dhclient"],
+               choices=["udhcpc", "dhclient", ""],
                help='DHCP client used by images to renew DCHP lease. '
                     'If left empty, update operation will be skipped. '
                     'Supported clients: "udhcpc", "dhclient"')