diff --git a/src/emqx_channel.erl b/src/emqx_channel.erl
index 37a2107db..7cfbd60d5 100644
--- a/src/emqx_channel.erl
+++ b/src/emqx_channel.erl
@@ -217,6 +217,9 @@ handle_in(?CONNECT_PACKET(ConnPkt), Channel) ->
             handle_out(connack, {ReasonCode, ConnPkt}, NChannel)
     end;
 
+handle_in(?PACKET(_), Channel = #channel{conn_state = ConnState}) when ConnState =/= connected ->
+    handle_out(disconnect, ?RC_PROTOCOL_ERROR, Channel);
+
 handle_in(Packet = ?PUBLISH_PACKET(_QoS), Channel) ->
     case emqx_packet:check(Packet) of
         ok -> process_publish(Packet, Channel);
diff --git a/test/emqx_channel_SUITE.erl b/test/emqx_channel_SUITE.erl
index b52d9ed07..412bafe80 100644
--- a/test/emqx_channel_SUITE.erl
+++ b/test/emqx_channel_SUITE.erl
@@ -112,6 +112,12 @@ t_handle_in_unexpected_connect_packet(_) ->
     {ok, [{outgoing, Packet}, {close, protocol_error}], Channel} =
         emqx_channel:handle_in(?CONNECT_PACKET(connpkt()), Channel).
 
+t_handle_in_unexpected_packet(_) ->
+    Channel = channel(),
+    Packet = ?DISCONNECT_PACKET(?RC_PROTOCOL_ERROR),
+    {ok, [{outgoing, Packet}, {close, protocol_error}], Channel} =
+        emqx_channel:handle_in(?PUBLISH_PACKET(?QOS_0), Channel).
+
 t_handle_in_qos0_publish(_) ->
     ok = meck:expect(emqx_broker, publish, fun(_) -> [] end),
     Channel = channel(#{conn_state => connected}),