diff --git a/apps/emqx_modules/src/emqx_delayed.erl b/apps/emqx_modules/src/emqx_delayed.erl
index db6226c1f..317942122 100644
--- a/apps/emqx_modules/src/emqx_delayed.erl
+++ b/apps/emqx_modules/src/emqx_delayed.erl
@@ -19,6 +19,7 @@
 -behaviour(gen_server).
 
 -include_lib("emqx/include/emqx.hrl").
+-include_lib("emqx/include/types.hrl").
 -include_lib("emqx/include/logger.hrl").
 
 %% Mnesia bootstrap
@@ -57,6 +58,14 @@
 -record(delayed_message, {key, delayed, msg}).
 -type delayed_message() :: #delayed_message{}.
 
+
+-type state() :: #{ publish_timer := maybe(timer:tref())
+                  , publish_at := non_neg_integer()
+                  , stats_timer := maybe(reference())
+                  , stats_fun := maybe(fun((pos_integer()) -> ok))
+                  , max_delayed_messages := non_neg_integer()
+                  }.
+
 %% sync ms with record change
 -define(QUERY_MS(Id), [{{delayed_message, {'_', Id}, '_', '_'}, [], ['$_']}]).
 -define(DELETE_MS(Id), [{{delayed_message, {'$1', Id}, '_', '_'}, [], ['$1']}]).
@@ -226,8 +235,10 @@ init([Opts]) ->
     emqx_conf:add_handler([delayed], ?MODULE),
     MaxDelayedMessages = maps:get(max_delayed_messages, Opts, 0),
     {ok, ensure_stats_event(
-           ensure_publish_timer(#{timer => undefined,
+           ensure_publish_timer(#{publish_timer => undefined,
                                   publish_at => 0,
+                                  stats_timer => undefined,
+                                  stats_fun => undefined,
                                   max_delayed_messages => MaxDelayedMessages}))}.
 
 handle_call({set_max_delayed_messages, Max}, _From, State) ->
@@ -268,10 +279,10 @@ handle_cast(Msg, State) ->
     {noreply, State}.
 
 %% Do Publish...
-handle_info({timeout, TRef, do_publish}, State = #{timer := TRef}) ->
+handle_info({timeout, TRef, do_publish}, State = #{publish_timer := TRef}) ->
     DeletedKeys = do_publish(mnesia:dirty_first(?TAB), os:system_time(seconds)),
     lists:foreach(fun(Key) -> mria:dirty_delete(?TAB, Key) end, DeletedKeys),
-    {noreply, ensure_publish_timer(State#{timer := undefined, publish_at := 0})};
+    {noreply, ensure_publish_timer(State#{publish_timer := undefined, publish_at := 0})};
 
 handle_info(stats, State = #{stats_fun := StatsFun}) ->
     StatsTimer = erlang:send_after(timer:seconds(1), self(), stats),
@@ -282,9 +293,10 @@ handle_info(Info, State) ->
     ?SLOG(error, #{msg => "unexpected_info", info => Info}),
     {noreply, State}.
 
-terminate(_Reason, #{stats_timer := TRef}) ->
+terminate(_Reason, #{publish_timer := PublishTimer, stats_timer := StatsTimer}) ->
     emqx_conf:remove_handler([delayed]),
-    emqx_misc:cancel_timer(TRef).
+    emqx_misc:cancel_timer(PublishTimer),
+    emqx_misc:cancel_timer(StatsTimer).
 
 code_change(_Vsn, State, _Extra) ->
     {ok, State}.
@@ -294,20 +306,22 @@ code_change(_Vsn, State, _Extra) ->
 %%--------------------------------------------------------------------
 
 %% Ensure the stats
+-spec ensure_stats_event(state()) -> state().
 ensure_stats_event(State) ->
     StatsFun = emqx_stats:statsfun('delayed.count', 'delayed.max'),
     StatsTimer = erlang:send_after(timer:seconds(1), self(), stats),
-    State#{stats_fun => StatsFun, stats_timer => StatsTimer}.
+    State#{stats_fun := StatsFun, stats_timer := StatsTimer}.
 
 %% Ensure publish timer
+-spec ensure_publish_timer(state()) -> state().
 ensure_publish_timer(State) ->
     ensure_publish_timer(mnesia:dirty_first(?TAB), State).
 
 ensure_publish_timer('$end_of_table', State) ->
-    State#{timer := undefined, publish_at := 0};
-ensure_publish_timer({Ts, _Id}, State = #{timer := undefined}) ->
+    State#{publish_timer := undefined, publish_at := 0};
+ensure_publish_timer({Ts, _Id}, State = #{publish_timer := undefined}) ->
     ensure_publish_timer(Ts, os:system_time(seconds), State);
-ensure_publish_timer({Ts, _Id}, State = #{timer := TRef, publish_at := PubAt})
+ensure_publish_timer({Ts, _Id}, State = #{publish_timer := TRef, publish_at := PubAt})
     when Ts < PubAt ->
     ok = emqx_misc:cancel_timer(TRef),
     ensure_publish_timer(Ts, os:system_time(seconds), State);
@@ -317,7 +331,7 @@ ensure_publish_timer(_Key, State) ->
 ensure_publish_timer(Ts, Now, State) ->
     Interval = max(1, Ts - Now),
     TRef = emqx_misc:start_timer(timer:seconds(Interval), do_publish),
-    State#{timer := TRef, publish_at := Now + Interval}.
+    State#{publish_timer := TRef, publish_at := Now + Interval}.
 
 do_publish(Key, Now) ->
     do_publish(Key, Now, []).