diff --git a/mysql-test/r/func_json.result b/mysql-test/r/func_json.result
index 0c60c42ec77..5c3134b7ce9 100644
--- a/mysql-test/r/func_json.result
+++ b/mysql-test/r/func_json.result
@@ -699,3 +699,9 @@ select @str, @path, JSON_EXTRACT(@str, @path);
 select json_array(5,json_query('[1,2]','$'));
 json_array(5,json_query('[1,2]','$'))
 [5, [1,2]]
+SELECT JSON_ARRAY('1. ě 2. š 3. č 4. ř 5. ž 6. ý 7. á 8. í 9. é 10. ů 11. ú') AS json_data;
+json_data
+["1. ě 2. š 3. č 4. ř 5. ž 6. ý 7. á 8. í 9. é 10. ů 11. ú"]
+SELECT JSON_OBJECT("user","Jožko Mrkvičká") as json_data;
+json_data
+{"user": "Jožko Mrkvičká"}
diff --git a/mysql-test/t/func_json.test b/mysql-test/t/func_json.test
index 39e31b8bb58..c660cb14856 100644
--- a/mysql-test/t/func_json.test
+++ b/mysql-test/t/func_json.test
@@ -354,3 +354,9 @@ select @str, @path, JSON_EXTRACT(@str, @path);
 #
 select json_array(5,json_query('[1,2]','$'));
 
+#
+# MDEV-13633 JSON_ARRAY() - bad output with some UTF8 characters.
+#
+
+SELECT JSON_ARRAY('1. ě 2. š 3. č 4. ř 5. ž 6. ý 7. á 8. í 9. é 10. ů 11. ú') AS json_data;
+SELECT JSON_OBJECT("user","Jožko Mrkvičká") as json_data;
diff --git a/sql/item_jsonfunc.cc b/sql/item_jsonfunc.cc
index a39b5f3f263..6398929defc 100644
--- a/sql/item_jsonfunc.cc
+++ b/sql/item_jsonfunc.cc
@@ -1473,6 +1473,7 @@ String *Item_func_json_array::val_str(String *str)
   uint n_arg;
 
   str->length(0);
+  str->set_charset(collation.collation);
 
   if (str->append("[", 1) ||
       ((arg_count > 0) && append_json_value(str, args[0], &tmp_val)))
@@ -1797,6 +1798,7 @@ String *Item_func_json_object::val_str(String *str)
   uint n_arg;
 
   str->length(0);
+  str->set_charset(collation.collation);
 
   if (str->append("{", 1) ||
       (arg_count > 0 &&