diff --git a/apps/emqx_authn/src/simple_authn/emqx_authn_pgsql.erl b/apps/emqx_authn/src/simple_authn/emqx_authn_pgsql.erl
index 89c489d6d..57a8416df 100644
--- a/apps/emqx_authn/src/simple_authn/emqx_authn_pgsql.erl
+++ b/apps/emqx_authn/src/simple_authn/emqx_authn_pgsql.erl
@@ -134,7 +134,7 @@ destroy(#{'_unique' := Unique}) ->
 parse_query(Query) ->
     case re:run(Query, ?RE_PLACEHOLDER, [global, {capture, all, binary}]) of
         {match, Captured} ->
-            PlaceHolders = [PlaceHolder || ["\\" ++ PlaceHolder] <- Captured],
+            PlaceHolders = ["\\" ++ PlaceHolder || [PlaceHolder] <- Captured],
             Replacements = ["$" ++ integer_to_list(I) || I <- lists:seq(1, length(Captured))],
             NQuery = lists:foldl(fun({PlaceHolder, Replacement}, Query0) ->
                                      re:replace(Query0, PlaceHolder, Replacement, [{return, binary}])