diff --git a/apps/emqx_rule_engine/src/emqx_rule_engine_api.erl b/apps/emqx_rule_engine/src/emqx_rule_engine_api.erl
index e40ef4a96..2e3a09172 100644
--- a/apps/emqx_rule_engine/src/emqx_rule_engine_api.erl
+++ b/apps/emqx_rule_engine/src/emqx_rule_engine_api.erl
@@ -86,7 +86,7 @@ api_spec() ->
 paths() -> ["/rule_events", "/rule_test", "/rules", "/rules/:id"].
 
 error_schema(Code, Message) when is_atom(Code) ->
-    emqx_dashboard_swagger:error_codes([Code], Message).
+    emqx_dashboard_swagger:error_codes([Code], list_to_binary(Message)).
 
 rule_creation_schema() ->
     ref(emqx_rule_api_schema, "rule_creation").
diff --git a/apps/emqx_rule_engine/src/emqx_rule_sqltester.erl b/apps/emqx_rule_engine/src/emqx_rule_sqltester.erl
index e1f135008..abd6a54c3 100644
--- a/apps/emqx_rule_engine/src/emqx_rule_sqltester.erl
+++ b/apps/emqx_rule_engine/src/emqx_rule_sqltester.erl
@@ -22,7 +22,7 @@
         , get_selected_data/3
         ]).
 
--spec test(#{sql := binary(), context := map()}) -> {ok, map() | list()} | {error, nomatch}.
+-spec test(#{sql := binary(), context := map()}) -> {ok, map() | list()} | {error, term()}.
 test(#{sql := Sql, context := Context}) ->
     case emqx_rule_sqlparser:parse(Sql) of
         {ok, Select} ->