diff --git a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
index c77ede7a3..f26143219 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
@@ -72,21 +72,22 @@ check_compat(Dump1, Dump2) ->
 check_api_immutability(#{release := Rel1, api := APIs1}, #{release := Rel2, api := APIs2})
   when Rel2 >= Rel1 ->
     %% TODO: Handle API deprecation
-    maps:map(fun(Key = {API, Version}, Val) ->
-                         case maps:get(Key, APIs2, undefined) of
-                             Val ->
-                                 ok;
-                             undefined ->
-                                 setnok(),
-                                 ?ERROR("API ~p v~p was removed in release ~p without being deprecated.",
-                                        [API, Version, Rel2]);
-                             _Val ->
-                                 setnok(),
-                                 ?ERROR("API ~p v~p was changed between ~p and ~p. Backplane API should be immutable.",
-                                        [API, Version, Rel1, Rel2])
-                         end
-                 end,
-                 APIs1),
+    _ = maps:map(
+          fun(Key = {API, Version}, Val) ->
+                  case maps:get(Key, APIs2, undefined) of
+                      Val ->
+                          ok;
+                      undefined ->
+                          setnok(),
+                          ?ERROR("API ~p v~p was removed in release ~p without being deprecated.",
+                                 [API, Version, Rel2]);
+                      _Val ->
+                          setnok(),
+                          ?ERROR("API ~p v~p was changed between ~p and ~p. Backplane API should be immutable.",
+                                 [API, Version, Rel1, Rel2])
+                  end
+          end,
+          APIs1),
     ok;
 check_api_immutability(_, _) ->
     ok.
diff --git a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
index 311edf399..a2ef547c0 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
@@ -31,7 +31,7 @@
         , module           :: atom()
         , version          :: non_neg_integer() | undefined
         , targets = []     :: [{semantics(), emqx_bpapi:call(), emqx_bpapi:call()}]
-        , errors = []      :: [string()]
+        , errors = []      :: list()
         , file
         }).
 
@@ -120,7 +120,7 @@ analyze_exprs(Line, Name, Arity, Head, Exprs, S) ->
             invalid_fun(Line, Name, Arity, S)
     end.
 
--spec extract_outer_args(erl_parse:abstract_form()) -> [atom()].
+-spec extract_outer_args([erl_parse:abstract_form()]) -> [atom()].
 extract_outer_args(Abs) ->
     lists:map(fun({var, _, Var}) ->
                       Var;
@@ -131,8 +131,7 @@ extract_outer_args(Abs) ->
               end,
               Abs).
 
--spec extract_target_call(Abs, [Abs]) -> {semantics(), emqx_bpapi:call()}
-              when Abs :: erl_parse:abstract_form().
+-spec extract_target_call(_AST, [_AST]) -> {semantics(), emqx_bpapi:call()}.
 extract_target_call(RPCBackend, OuterArgs) ->
     {Semantics, {atom, _, M}, {atom, _, F}, A} = extract_mfa(RPCBackend, OuterArgs),
     {Semantics, {M, F, list_to_args(A)}}.
@@ -140,8 +139,6 @@ extract_target_call(RPCBackend, OuterArgs) ->
 -define(BACKEND(MOD, FUN), {remote, _, {atom, _, MOD}, {atom, _, FUN}}).
 -define(IS_RPC(MOD), (MOD =:= erpc orelse MOD =:= rpc)).
 
--spec extract_mfa(Abs, #s{}) -> {call | cast, Abs, Abs, Abs}
-              when Abs :: erl_parse:abstract_form().
 %% gen_rpc:
 extract_mfa(?BACKEND(gen_rpc, _), _) ->
     %% gen_rpc has an extremely messy API, thankfully it's fully wrapped