diff --git a/hbmqtt/mqtt/protocol/broker_handler.py b/hbmqtt/mqtt/protocol/broker_handler.py
index 3f0935f..39b2a2a 100644
--- a/hbmqtt/mqtt/protocol/broker_handler.py
+++ b/hbmqtt/mqtt/protocol/broker_handler.py
@@ -145,6 +145,10 @@ class BrokerProtocolHandler(ProtocolHandler):
             error_msg = 'Invalid protocol from %s: %d' % \
                               (format_client_message(address=remote_address, port=remote_port), connect.proto_level)
             connack = ConnackPacket.build(0, UNACCEPTABLE_PROTOCOL_VERSION)  # [MQTT-3.2.2-4] session_parent=0
+        elif not connect.username_flag and connect.password_flag:
+            connack = ConnackPacket.build(0, BAD_USERNAME_PASSWORD)  # [MQTT-3.1.2-22]
+        elif connect.username_flag and not connect.password_flag:
+            connack = ConnackPacket.build(0, BAD_USERNAME_PASSWORD)  # [MQTT-3.1.2-22]
         elif connect.username_flag and connect.username is None:
             error_msg = 'Invalid username from %s' % \
                               (format_client_message(address=remote_address, port=remote_port))