diff --git a/UPGRADING.INTERNALS b/UPGRADING.INTERNALS
index bbcc1223c634a..ec2c57854ecca 100644
--- a/UPGRADING.INTERNALS
+++ b/UPGRADING.INTERNALS
@@ -376,6 +376,10 @@ PHP 8.4 INTERNALS UPGRADE NOTES
    - The deprecated php_uint32 and php_int32 typedefs have been removed from
      ext/standard/basic_functions.h. Use the standard uint32_t and int32_t
      types instead.
+   - The php_strtoupper(), php_string_toupper(), php_strtolower(), and
+     php_string_tolower() functions has been removed, use zend_str_toupper(),
+     zend_string_toupper(), zend_str_tolower(), and zend_string_tolower()
+     respectively instead.
 
  h. ext/session
    - Added the php_get_session_status() API to get the session status, which is
diff --git a/ext/standard/php_string.h b/ext/standard/php_string.h
index f00ff830682ce..afb156ad7d8b2 100644
--- a/ext/standard/php_string.h
+++ b/ext/standard/php_string.h
@@ -34,10 +34,6 @@ PHP_MINIT_FUNCTION(string_intrin);
 	strnatcmp_ex(a, strlen(a), b, strlen(b), 1)
 PHPAPI int strnatcmp_ex(char const *a, size_t a_len, char const *b, size_t b_len, bool is_case_insensitive);
 PHPAPI struct lconv *localeconv_r(struct lconv *out);
-PHPAPI char *php_strtoupper(char *s, size_t len);
-PHPAPI char *php_strtolower(char *s, size_t len);
-PHPAPI zend_string *php_string_toupper(zend_string *s);
-PHPAPI zend_string *php_string_tolower(zend_string *s);
 PHPAPI char *php_strtr(char *str, size_t len, const char *str_from, const char *str_to, size_t trlen);
 PHPAPI zend_string *php_addslashes(zend_string *str);
 PHPAPI void php_stripslashes(zend_string *str);
diff --git a/ext/standard/string.c b/ext/standard/string.c
index 70b5ffd0bd0e9..6ebe7db08965f 100644
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -1211,21 +1211,6 @@ PHP_FUNCTION(strtok)
 }
 /* }}} */
 
-/* {{{ php_strtoupper */
-PHPAPI char *php_strtoupper(char *s, size_t len)
-{
-	zend_str_toupper(s, len);
-	return s;
-}
-/* }}} */
-
-/* {{{ php_string_toupper */
-PHPAPI zend_string *php_string_toupper(zend_string *s)
-{
-	return zend_string_toupper(s);
-}
-/* }}} */
-
 /* {{{ Makes a string uppercase */
 PHP_FUNCTION(strtoupper)
 {
@@ -1239,21 +1224,6 @@ PHP_FUNCTION(strtoupper)
 }
 /* }}} */
 
-/* {{{ php_strtolower */
-PHPAPI char *php_strtolower(char *s, size_t len)
-{
-	zend_str_tolower(s, len);
-	return s;
-}
-/* }}} */
-
-/* {{{ php_string_tolower */
-PHPAPI zend_string *php_string_tolower(zend_string *s)
-{
-	return zend_string_tolower(s);
-}
-/* }}} */
-
 /* {{{ Makes a string lowercase */
 PHP_FUNCTION(strtolower)
 {