diff --git a/apps/emqx/src/emqx_os_mon.erl b/apps/emqx/src/emqx_os_mon.erl
index dfce7a255..fdcdf82b3 100644
--- a/apps/emqx/src/emqx_os_mon.erl
+++ b/apps/emqx/src/emqx_os_mon.erl
@@ -85,11 +85,10 @@ init([]) ->
     {ok, #{}}.
 
 handle_call(Req, _From, State) ->
-    ?LOG(error, "Unexpected call: ~p", [Req]),
-    {reply, ignored, State}.
+    {reply, {error, {unexpected_call, Req}}, State}.
 
 handle_cast(Msg, State) ->
-    ?LOG(error, "Unexpected cast: ~p", [Msg]),
+    ?LOG(error, "unexpected_cast_discarded: ~p", [Msg]),
     {noreply, State}.
 
 handle_info({timeout, _Timer, check}, State) ->
@@ -111,7 +110,7 @@ handle_info({timeout, _Timer, check}, State) ->
     {noreply, State};
 
 handle_info(Info, State) ->
-    ?LOG(error, "unexpected info: ~p", [Info]),
+    ?LOG(info, "unexpected_info_discarded: ~p", [Info]),
     {noreply, State}.
 
 terminate(_Reason, _State) ->
diff --git a/apps/emqx/test/emqx_os_mon_SUITE.erl b/apps/emqx/test/emqx_os_mon_SUITE.erl
index 56c81e9e6..674d005d3 100644
--- a/apps/emqx/test/emqx_os_mon_SUITE.erl
+++ b/apps/emqx/test/emqx_os_mon_SUITE.erl
@@ -52,7 +52,8 @@ t_api(_) ->
     ?assertEqual(ok, emqx_os_mon:set_procmem_high_watermark(0.11)),
     ?assertEqual(11, emqx_os_mon:get_procmem_high_watermark()),
 
-    ?assertEqual(ignored, gen_server:call(emqx_os_mon, ignored)),
+    ?assertEqual({error, {unexpected_call, ignored}},
+                 gen_server:call(emqx_os_mon, ignored)),
     ?assertEqual(ok, gen_server:cast(emqx_os_mon, ignored)),
     emqx_os_mon ! ignored,
     gen_server:stop(emqx_os_mon),