diff --git a/zulip_botserver/zulip_botserver/server.py b/zulip_botserver/zulip_botserver/server.py
index 3ca019f..45d6680 100644
--- a/zulip_botserver/zulip_botserver/server.py
+++ b/zulip_botserver/zulip_botserver/server.py
@@ -12,6 +12,7 @@ from werkzeug.exceptions import BadRequest
 from six.moves.configparser import SafeConfigParser
 
 from zulip import Client
+from zulip_bots.custom_exceptions import ConfigValidationError
 from zulip_bots.lib import ExternalBotHandler, StateHandler
 
 bots_config = {}  # type: Dict[str, Mapping[str, str]]