diff --git a/src/backend/utils/adt/jsonb.c b/src/backend/utils/adt/jsonb.c
index e4562b3c6ce..b6110abaa52 100644
--- a/src/backend/utils/adt/jsonb.c
+++ b/src/backend/utils/adt/jsonb.c
@@ -657,7 +657,7 @@ datum_to_jsonb_internal(Datum val, bool is_null, JsonbInState *result,
 			  tcategory == JSONTYPE_COMPOSITE ||
 			  tcategory == JSONTYPE_JSON ||
 			  tcategory == JSONTYPE_JSONB ||
-			  tcategory == JSONTYPE_JSON))
+			  tcategory == JSONTYPE_CAST))
 	{
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
diff --git a/src/test/regress/expected/sqljson.out b/src/test/regress/expected/sqljson.out
index e25a49928bc..17a889eb8ef 100644
--- a/src/test/regress/expected/sqljson.out
+++ b/src/test/regress/expected/sqljson.out
@@ -571,6 +571,18 @@ SELECT JSON_OBJECT(1: 1, '2': NULL, '3': 1, 4: NULL, '5': 'a' ABSENT ON NULL WIT
  {"1": 1, "3": 1, "5": "a"}
 (1 row)
 
+-- BUG: https://postgr.es/m/CADXhmgTJtJZK9A3Na_ry%2BXrq-ghjcejBRhcRMzWZvbd__QdgJA%40mail.gmail.com
+-- datum_to_jsonb_internal() didn't catch keys that are casts instead of a simple scalar
+CREATE TYPE mood AS ENUM ('happy', 'sad', 'neutral');
+CREATE FUNCTION mood_to_json(mood) RETURNS json AS $$
+  SELECT to_json($1::text);
+$$ LANGUAGE sql IMMUTABLE;
+CREATE CAST (mood AS json) WITH FUNCTION mood_to_json(mood) AS IMPLICIT;
+SELECT JSON_OBJECT('happy'::mood: '123'::jsonb);
+ERROR:  key value must be scalar, not array, composite, or json
+DROP CAST (mood AS json);
+DROP FUNCTION mood_to_json;
+DROP TYPE mood;
 -- JSON_ARRAY()
 SELECT JSON_ARRAY();
  json_array 
diff --git a/src/test/regress/sql/sqljson.sql b/src/test/regress/sql/sqljson.sql
index 9b5d82602d0..3fd6ac260b8 100644
--- a/src/test/regress/sql/sqljson.sql
+++ b/src/test/regress/sql/sqljson.sql
@@ -152,6 +152,17 @@ SELECT JSON_OBJECT(1: 1, '2': NULL, '1': 1 ABSENT ON NULL WITH UNIQUE RETURNING
 SELECT JSON_OBJECT(1: 1, '2': NULL, '1': 1 ABSENT ON NULL WITHOUT UNIQUE RETURNING jsonb);
 SELECT JSON_OBJECT(1: 1, '2': NULL, '3': 1, 4: NULL, '5': 'a' ABSENT ON NULL WITH UNIQUE RETURNING jsonb);
 
+-- BUG: https://postgr.es/m/CADXhmgTJtJZK9A3Na_ry%2BXrq-ghjcejBRhcRMzWZvbd__QdgJA%40mail.gmail.com
+-- datum_to_jsonb_internal() didn't catch keys that are casts instead of a simple scalar
+CREATE TYPE mood AS ENUM ('happy', 'sad', 'neutral');
+CREATE FUNCTION mood_to_json(mood) RETURNS json AS $$
+  SELECT to_json($1::text);
+$$ LANGUAGE sql IMMUTABLE;
+CREATE CAST (mood AS json) WITH FUNCTION mood_to_json(mood) AS IMPLICIT;
+SELECT JSON_OBJECT('happy'::mood: '123'::jsonb);
+DROP CAST (mood AS json);
+DROP FUNCTION mood_to_json;
+DROP TYPE mood;
 
 -- JSON_ARRAY()
 SELECT JSON_ARRAY();