diff --git a/zulip_botserver/zulip_botserver/server.py b/zulip_botserver/zulip_botserver/server.py
index c6a9a00..04b423c 100644
--- a/zulip_botserver/zulip_botserver/server.py
+++ b/zulip_botserver/zulip_botserver/server.py
@@ -140,7 +140,7 @@ bots_config = {}  # type: Dict[str, Dict[str, str]]
 
 
 @app.route('/', methods=['POST'])
-def handle_bot() -> Union[str, BadRequest, Unauthorized]:
+def handle_bot() -> str:
     event = request.get_json(force=True)
     for bot_name, config in bots_config.items():
         if config['email'] == event['bot_email']:
@@ -148,13 +148,13 @@ def handle_bot() -> Union[str, BadRequest, Unauthorized]:
             bot_config = config
             break
     else:
-        return BadRequest("Cannot find a bot with email {} in the Botserver "
-                          "configuration file. Do the emails in your botserverrc "
-                          "match the bot emails on the server?".format(event['bot_email']))
+        raise BadRequest("Cannot find a bot with email {} in the Botserver "
+                         "configuration file. Do the emails in your botserverrc "
+                         "match the bot emails on the server?".format(event['bot_email']))
     if bot_config['token'] != event['token']:
-        return Unauthorized("Request token does not match token found for bot {} in the "
-                            "Botserver configuration file. Do the outgoing webhooks in "
-                            "Zulip point to the right Botserver?".format(event['bot_email']))
+        raise Unauthorized("Request token does not match token found for bot {} in the "
+                           "Botserver configuration file. Do the outgoing webhooks in "
+                           "Zulip point to the right Botserver?".format(event['bot_email']))
     lib_module = app.config.get("BOTS_LIB_MODULES", {})[bot]
     bot_handler = app.config.get("BOT_HANDLERS", {})[bot]
     message_handler = app.config.get("MESSAGE_HANDLERS", {})[bot]