diff --git a/src/emqttd_mqueue.erl b/src/emqttd_mqueue.erl
index 53f37206f..9abcc6843 100644
--- a/src/emqttd_mqueue.erl
+++ b/src/emqttd_mqueue.erl
@@ -1,5 +1,5 @@
 %%--------------------------------------------------------------------
-%% Copyright (c) 2012-2017 Feng Lee <feng@emqtt.io>.
+%% Copyright (c) 2013-2017 EMQ Enterprise, Inc. (http://emqtt.io)
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -43,35 +43,33 @@
 
 -module(emqttd_mqueue).
 
+-author("Feng Lee <feng@emqtt.io>").
+
 -include("emqttd.hrl").
 
 -include("emqttd_protocol.hrl").
 
 -import(proplists, [get_value/3]).
 
--export([new/3, type/1, name/1, is_empty/1, len/1, max_len/1, in/2, out/1, stats/1]).
+-export([new/3, type/1, name/1, is_empty/1, len/1, max_len/1, in/2, out/1,
+         dropped/1, stats/1]).
 
 -define(LOW_WM, 0.2).
 
 -define(HIGH_WM, 0.6).
 
--type priority() :: {iolist(), pos_integer()}.
+-type(priority() :: {iolist(), pos_integer()}).
 
--type option() :: {type, simple | priority}
+-type(option() :: {type, simple | priority}
                 | {max_length, pos_integer() | infinity}
                 | {priority, list(priority())}
-                | {low_watermark, float()}     %% Low watermark
-                | {high_watermark, float()}    %% High watermark
-                | {queue_qos0, boolean()}.     %% Queue Qos0?
+                | {low_watermark, float()}  %% Low watermark
+                | {high_watermark, float()} %% High watermark
+                | {queue_qos0, boolean()}). %% Queue Qos0?
 
--type mqueue_option() :: {max_length, pos_integer()} %% Max queue length
-                       | {low_watermark, float()}    %% Low watermark
-                       | {high_watermark, float()}   %% High watermark
-                       | {queue_qos0, boolean()}.    %% Queue Qos0
-
--type stat() :: {max_len, infinity | pos_integer()}
+-type(stat() :: {max_len, infinity | pos_integer()}
               | {len, non_neg_integer()}
-              | {dropped, non_neg_integer()}.
+              | {dropped, non_neg_integer()}).
 
 -record(mqueue, {type :: simple | priority,
                  name, q :: queue:queue() | priority_queue:q(),
@@ -83,12 +81,12 @@
                  qos0 = false, dropped = 0,
                  alarm_fun}).
 
--type mqueue() :: #mqueue{}.
+-type(mqueue() :: #mqueue{}).
 
 -export_type([mqueue/0, priority/0, option/0]).
 
 %% @doc New Queue.
--spec(new(iolist(), list(mqueue_option()), fun()) -> mqueue()).
+-spec(new(iolist(), list(option()), fun()) -> mqueue()).
 new(Name, Opts, AlarmFun) ->
     Type = get_value(type, Opts, simple),
     MaxLen = get_value(max_length, Opts, infinity),
@@ -141,6 +139,10 @@ len(#mqueue{type = priority, q = Q})   -> priority_queue:len(Q).
 
 max_len(#mqueue{max_len= MaxLen}) -> MaxLen.
 
+%% @doc Dropped of the mqueue
+-spec(dropped(mqueue()) -> non_neg_integer()).
+dropped(#mqueue{dropped = Dropped}) -> Dropped.
+
 %% @doc Stats of the mqueue
 -spec(stats(mqueue()) -> [stat()]).
 stats(#mqueue{type = Type, q = Q, max_len = MaxLen, len = Len, dropped = Dropped}) ->
@@ -208,14 +210,12 @@ maybe_set_alarm(MQ = #mqueue{name = Name, len = Len, high_wm = HighWM, alarm_fun
                         title = io_lib:format("Queue ~s high-water mark", [Name]),
                         summary = io_lib:format("queue len ~p > high_watermark ~p", [Len, HighWM])},
     MQ#mqueue{alarm_fun = AlarmFun(alert, Alarm)};
-
 maybe_set_alarm(MQ) ->
     MQ.
 
 maybe_clear_alarm(MQ = #mqueue{name = Name, len = Len, low_wm = LowWM, alarm_fun = AlarmFun})
     when Len < LowWM ->
     MQ#mqueue{alarm_fun = AlarmFun(clear, list_to_binary(["queue_high_watermark.", Name]))};
-
 maybe_clear_alarm(MQ) ->
     MQ.