diff --git a/apps/emqx_sn/src/emqx_sn_gateway.erl b/apps/emqx_sn/src/emqx_sn_gateway.erl
index 9828ed383..a1e062add 100644
--- a/apps/emqx_sn/src/emqx_sn_gateway.erl
+++ b/apps/emqx_sn/src/emqx_sn_gateway.erl
@@ -74,7 +74,7 @@
                 sockstate            :: emqx_types:sockstate(),
                 sockname             :: {inet:ip_address(), inet:port()},
                 peername             :: {inet:ip_address(), inet:port()},
-                channel              :: emqx_channel:channel(),
+                channel              :: maybe(emqx_channel:channel()),
                 registry             :: emqx_sn_registry:registry(),
                 clientid             :: maybe(binary()),
                 username             :: maybe(binary()),
@@ -105,6 +105,8 @@
 
 -define(NO_PEERCERT, undefined).
 
+%% TODO: fix when https://github.com/emqx/emqx-sn/pull/170 is merged
+-dialyzer([{nowarn_function, [idle/3]}]).
 
 %%--------------------------------------------------------------------
 %% Exported APIs
@@ -136,7 +138,8 @@ init([{_, SockPid, Sock}, Peername, Options]) ->
     EnableStats = proplists:get_value(enable_stats, Options, false),
     case inet:sockname(Sock) of
         {ok, Sockname} ->
-            Channel = emqx_channel:init(#{sockname => Sockname,
+            Channel = emqx_channel:init(#{socktype => udp,
+                                          sockname => Sockname,
                                           peername => Peername,
                                           protocol => 'mqtt-sn',
                                           peercert => ?NO_PEERCERT,
@@ -195,14 +198,18 @@ idle(cast, {incoming, ?SN_PUBLISH_MSG(_Flag, _TopicId, _MsgId, _Data)}, State =
 idle(cast, {incoming, ?SN_PUBLISH_MSG(#mqtt_sn_flags{qos = ?QOS_NEG1,
                                                      topic_id_type = TopicIdType
                                                     }, TopicId, _MsgId, Data)},
-     State = #state{clientid = ClientId, registry = Registry}) ->
+    State = #state{clientid = ClientId, registry = Registry}) ->
     TopicName = case (TopicIdType =:= ?SN_SHORT_TOPIC) of
-                    false ->
-                        emqx_sn_registry:lookup_topic(Registry, ClientId, TopicId);
+                    false -> emqx_sn_registry:lookup_topic(Registry, ClientId, TopicId);
                     true  -> <<TopicId:16>>
                 end,
-    Msg = emqx_message:make(?NEG_QOS_CLIENT_ID, ?QOS_0, TopicName, Data),
-    (TopicName =/= undefined) andalso emqx_broker:publish(Msg),
+    case TopicName =/= undefined of
+        true ->
+            Msg = emqx_message:make(?NEG_QOS_CLIENT_ID, ?QOS_0, TopicName, Data),
+            emqx_broker:publish(Msg);
+        false ->
+            ok
+    end;
     ?LOG(debug, "Client id=~p receives a publish with QoS=-1 in idle mode!", [ClientId], State),
     {keep_state_and_data, State#state.idle_timeout};
 
@@ -562,10 +569,9 @@ terminate(Reason, _StateName, #state{clientid = ClientId,
                                      channel  = Channel,
                                      registry = Registry}) ->
     emqx_sn_registry:unregister_topic(Registry, ClientId),
-    case {Channel, Reason} of
-        {undefined, _} -> ok;
-        {_, _} ->
-            emqx_channel:terminate(Reason, Channel)
+    case Channel =:= undefined of
+        true -> ok;
+        false -> emqx_channel:terminate(Reason, Channel)
     end.
 
 code_change(_Vsn, StateName, State, _Extra) ->
diff --git a/src/emqx_types.erl b/src/emqx_types.erl
index c1d3822cb..dd1bd71a9 100644
--- a/src/emqx_types.erl
+++ b/src/emqx_types.erl
@@ -148,7 +148,8 @@
 -type(username() :: maybe(binary())).
 -type(password() :: maybe(binary())).
 -type(peerhost() :: inet:ip_address()).
--type(peername() :: {inet:ip_address(), inet:port_number()}).
+-type(peername() :: {inet:ip_address(), inet:port_number()}
+                  | inet:returned_non_ip_address()).
 -type(protocol() :: mqtt | 'mqtt-sn' | coap | lwm2m | stomp | none | atom()).
 -type(auth_result() :: success
                      | client_identifier_not_valid