diff --git a/src/emqx_alarm_handler.erl b/src/emqx_alarm_handler.erl
index 2131bd177..ceb34acb7 100644
--- a/src/emqx_alarm_handler.erl
+++ b/src/emqx_alarm_handler.erl
@@ -105,7 +105,7 @@ init(_) ->
     {ok, []}.
 
 handle_event({set_alarm, {AlarmId, AlarmDesc = #alarm{timestamp = undefined}}}, State) ->
-    handle_event({set_alarm, {AlarmId, AlarmDesc#alarm{timestamp = os:timestamp()}}}, State);
+    handle_event({set_alarm, {AlarmId, AlarmDesc#alarm{timestamp = erlang:system_time(second)}}}, State);
 handle_event({set_alarm, Alarm = {AlarmId, AlarmDesc}}, State) ->
     ?LOG(warning, "New Alarm: ~p, Alarm Info: ~p", [AlarmId, AlarmDesc]),
     case encode_alarm(Alarm) of
@@ -158,7 +158,7 @@ encode_alarm({AlarmId, #alarm{severity  = Severity,
                            {desc, [{severity, Severity},
                                    {title, iolist_to_binary(Title)},
                                    {summary, iolist_to_binary(Summary)},
-                                   {timestamp, emqx_misc:now_to_secs(Ts)}]}]);
+                                   {timestamp, Ts}]}]);
 encode_alarm({AlarmId, undefined}) ->
     emqx_json:safe_encode([{id, maybe_to_binary(AlarmId)}]);
 encode_alarm({AlarmId, AlarmDesc}) ->
@@ -194,5 +194,5 @@ clear_alarm_(Id) ->
 set_alarm_history(Id, Desc) ->
     His = #alarm_history{id = Id,
                          desc = Desc,
-                         clear_at = os:timestamp()},
+                         clear_at = erlang:system_time(second)},
     mnesia:dirty_write(?ALARM_HISTORY_TAB, His).
diff --git a/test/emqx_session_SUITE.erl b/test/emqx_session_SUITE.erl
index acfb817a2..fa4798391 100644
--- a/test/emqx_session_SUITE.erl
+++ b/test/emqx_session_SUITE.erl
@@ -141,13 +141,13 @@ t_is_awaiting_full_true(_) ->
 
 t_puback(_) ->
     Msg = emqx_message:make(test, ?QOS_1, <<"t">>, <<>>),
-    Inflight = emqx_inflight:insert(1, {Msg, os:timestamp()}, emqx_inflight:new()),
+    Inflight = emqx_inflight:insert(1, {Msg, erlang:system_time(millisecond)}, emqx_inflight:new()),
     Session = set_field(inflight, Inflight, session()),
     {ok, Msg, NSession} = emqx_session:puback(1, Session),
     ?assertEqual(0, emqx_session:info(inflight_cnt, NSession)).
 
 t_puback_error_packet_id_in_use(_) ->
-    Inflight = emqx_inflight:insert(1, {pubrel, os:timestamp()}, emqx_inflight:new()),
+    Inflight = emqx_inflight:insert(1, {pubrel, erlang:system_time(millisecond)}, emqx_inflight:new()),
     Session = set_field(inflight, Inflight, session()),
     {error, ?RC_PACKET_IDENTIFIER_IN_USE} = emqx_session:puback(1, Session).
 
@@ -156,13 +156,13 @@ t_puback_error_packet_id_not_found(_) ->
 
 t_pubrec(_) ->
     Msg = emqx_message:make(test, ?QOS_2, <<"t">>, <<>>),
-    Inflight = emqx_inflight:insert(2, {Msg, os:timestamp()}, emqx_inflight:new()),
+    Inflight = emqx_inflight:insert(2, {Msg, erlang:system_time(millisecond)}, emqx_inflight:new()),
     Session = set_field(inflight, Inflight, session()),
     {ok, Msg, NSession} = emqx_session:pubrec(2, Session),
     ?assertMatch([{pubrel, _}], emqx_inflight:values(emqx_session:info(inflight, NSession))).
 
 t_pubrec_packet_id_in_use_error(_) ->
-    Inflight = emqx_inflight:insert(1, {pubrel, ts()}, emqx_inflight:new()),
+    Inflight = emqx_inflight:insert(1, {pubrel, erlang:system_time(millisecond)}, emqx_inflight:new()),
     Session = set_field(inflight, Inflight, session()),
     {error, ?RC_PACKET_IDENTIFIER_IN_USE} = emqx_session:puback(1, Session).
 
@@ -170,7 +170,7 @@ t_pubrec_packet_id_not_found_error(_) ->
     {error, ?RC_PACKET_IDENTIFIER_NOT_FOUND} = emqx_session:pubrec(1, session()).
 
 t_pubrel(_) ->
-    Session = set_field(awaiting_rel, #{1 => os:timestamp()}, session()),
+    Session = set_field(awaiting_rel, #{1 => erlang:system_time(millisecond)}, session()),
     {ok, NSession} = emqx_session:pubrel(1, Session),
     ?assertEqual(#{}, emqx_session:info(awaiting_rel, NSession)).
 
@@ -178,7 +178,7 @@ t_pubrel_id_not_found(_) ->
     {error, ?RC_PACKET_IDENTIFIER_NOT_FOUND} = emqx_session:pubrel(1, session()).
 
 t_pubcomp(_) ->
-    Inflight = emqx_inflight:insert(2, {pubrel, os:timestamp()}, emqx_inflight:new()),
+    Inflight = emqx_inflight:insert(2, {pubrel, erlang:system_time(millisecond)}, emqx_inflight:new()),
     Session = emqx_session:set_field(inflight, Inflight, session()),
     {ok, NSession} = emqx_session:pubcomp(2, Session),
     ?assertEqual(0, emqx_session:info(inflight_cnt, NSession)).
@@ -252,5 +252,3 @@ subopts(Init) ->
 delivery(QoS, Topic) ->
     {deliver, Topic, emqx_message:make(test, QoS, Topic, <<"payload">>)}.
 
-ts() -> erlang:system_time(second).
-