diff --git a/src/test/regress/expected/pg15.out b/src/test/regress/expected/pg15.out
index 13a3bcd7b..57a095c12 100644
--- a/src/test/regress/expected/pg15.out
+++ b/src/test/regress/expected/pg15.out
@@ -1554,10 +1554,10 @@ CREATE DATABASE mydatabase
             CONNECTION LIMIT = 10
             ENCODING = 'UTF8'
             STRATEGY = 'wal_log'
-            LOCALE = 'en_US.UTF-8'
-            LC_COLLATE = 'en_US.UTF-8'
-            LC_CTYPE = 'en_US.UTF-8'
-            ICU_LOCALE = 'en_US.UTF-8'
+            LOCALE = 'en_US.utf-8'
+            LC_COLLATE = 'en_US.utf-8'
+            LC_CTYPE = 'en_US.utf-8'
+            ICU_LOCALE = 'en_US.utf-8'
             LOCALE_PROVIDER = 'icu'
             COLLATION_VERSION = '1.0'
             TABLESPACE = create_drop_db_tablespace
@@ -1574,7 +1574,7 @@ join pg_tablespace pt on pd.dattablespace = pt.oid
 WHERE datname = 'mydatabase';
   datname   | encoding | datlocprovider | datistemplate | datallowconn | datconnlimit | datcollate  |  datctype   | daticulocale | datcollversion | datacl |      database_owner      |      database_owner      |        tablespace
 ---------------------------------------------------------------------
- mydatabase |        6 | i              | f             | t            |           10 | en_US.UTF-8 | en_US.UTF-8 | en_US.UTF-8  | 1.0            |        | create_drop_db_test_user | create_drop_db_test_user | create_drop_db_tablespace
+ mydatabase |        6 | i              | f             | t            |           10 | en_US.utf-8 | en_US.utf-8 | en_US.utf-8  | 1.0            |        | create_drop_db_test_user | create_drop_db_test_user | create_drop_db_tablespace
 (1 row)
 
 \c - - - :worker_1_port
@@ -1588,7 +1588,7 @@ join pg_tablespace pt on pd.dattablespace = pt.oid
 WHERE datname = 'mydatabase';
   datname   | encoding | datlocprovider | datistemplate | datallowconn | datconnlimit | datcollate  |  datctype   | daticulocale | datcollversion | datacl |      database_owner      |      database_owner      |        tablespace
 ---------------------------------------------------------------------
- mydatabase |        6 | i              | f             | t            |           10 | en_US.UTF-8 | en_US.UTF-8 | en_US.UTF-8  | 1.0            |        | create_drop_db_test_user | create_drop_db_test_user | create_drop_db_tablespace
+ mydatabase |        6 | i              | f             | t            |           10 | en_US.utf-8 | en_US.utf-8 | en_US.utf-8  | 1.0            |        | create_drop_db_test_user | create_drop_db_test_user | create_drop_db_tablespace
 (1 row)
 
 \c - - - :worker_2_port
@@ -1602,7 +1602,7 @@ join pg_tablespace pt on pd.dattablespace = pt.oid
 WHERE datname = 'mydatabase';
   datname   | encoding | datlocprovider | datistemplate | datallowconn | datconnlimit | datcollate  |  datctype   | daticulocale | datcollversion | datacl |      database_owner      |      database_owner      |        tablespace
 ---------------------------------------------------------------------
- mydatabase |        6 | i              | f             | t            |           10 | en_US.UTF-8 | en_US.UTF-8 | en_US.UTF-8  | 1.0            |        | create_drop_db_test_user | create_drop_db_test_user | create_drop_db_tablespace
+ mydatabase |        6 | i              | f             | t            |           10 | en_US.utf-8 | en_US.utf-8 | en_US.utf-8  | 1.0            |        | create_drop_db_test_user | create_drop_db_test_user | create_drop_db_tablespace
 (1 row)
 
 \c - - - :master_port
diff --git a/src/test/regress/sql/pg15.sql b/src/test/regress/sql/pg15.sql
index 86afdea2b..ac5f6eec1 100644
--- a/src/test/regress/sql/pg15.sql
+++ b/src/test/regress/sql/pg15.sql
@@ -1001,10 +1001,10 @@ CREATE DATABASE mydatabase
             CONNECTION LIMIT = 10
             ENCODING = 'UTF8'
             STRATEGY = 'wal_log'
-            LOCALE = 'en_US.UTF-8'
-            LC_COLLATE = 'en_US.UTF-8'
-            LC_CTYPE = 'en_US.UTF-8'
-            ICU_LOCALE = 'en_US.UTF-8'
+            LOCALE = 'en_US.utf-8'
+            LC_COLLATE = 'en_US.utf-8'
+            LC_CTYPE = 'en_US.utf-8'
+            ICU_LOCALE = 'en_US.utf-8'
             LOCALE_PROVIDER = 'icu'
             COLLATION_VERSION = '1.0'
             TABLESPACE = create_drop_db_tablespace