diff --git a/apps/emqx/src/emqx_sys_mon.erl b/apps/emqx/src/emqx_sys_mon.erl
index a5dab29b1..35c8035f0 100644
--- a/apps/emqx/src/emqx_sys_mon.erl
+++ b/apps/emqx/src/emqx_sys_mon.erl
@@ -193,9 +193,6 @@ procinfo(Pid) ->
 procinfo_l(undefined) -> [];
 procinfo_l(List) -> List.
 
-%% FIXME: impossible case in practice; it's always a PID
-get_proc_lib_initial_call(undefined) ->
-    [];
 get_proc_lib_initial_call(Pid) ->
     case proc_lib:initial_call(Pid) of
         false ->
diff --git a/apps/emqx/test/emqx_sys_mon_SUITE.erl b/apps/emqx/test/emqx_sys_mon_SUITE.erl
index 4c3839d11..b62aa16ef 100644
--- a/apps/emqx/test/emqx_sys_mon_SUITE.erl
+++ b/apps/emqx/test/emqx_sys_mon_SUITE.erl
@@ -88,11 +88,6 @@ end_per_testcase(_, _Config) ->
     emqx_common_test_helpers:stop_apps([]).
 
 t_procinfo(_) ->
-    ok = meck:expect(emqx_vm, get_process_info, fun(_) -> [] end),
-    ok = meck:expect(emqx_vm, get_process_gc_info, fun(_) -> [] end),
-    %% FIXME: `procinfo' will actually crash if `undefined' is passed
-    %% to it
-    ?assertEqual([{pid, undefined}], emqx_sys_mon:procinfo(undefined)),
     ok = meck:expect(emqx_vm, get_process_info, fun(_) -> [] end),
     ok = meck:expect(emqx_vm, get_process_gc_info, fun(_) -> undefined end),
     ?assertEqual([{pid, self()}], emqx_sys_mon:procinfo(self())).