diff --git a/UPGRADING b/UPGRADING
index cdada9e9b3273..ebadbb0a1f58d 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -76,6 +76,10 @@ PHP 8.3 UPGRADE NOTES
 - Dom:
   . Changed DOMCharacterData::appendData() tentative return type to true.
 
+- Intl:
+  . datefmt_set_timezone (and its alias IntlDateformatter::setTimeZone) 
+    now returns true on sucess, previously null was returned.
+
 - MBString:
   . mb_strtolower, mb_strtotitle, and mb_convert_case implement conditional
     casing rules for the Greek letter sigma. For mb_convert_case, conditional
diff --git a/ext/intl/dateformat/dateformat.stub.php b/ext/intl/dateformat/dateformat.stub.php
index ed49bcc0d89a9..3e5f178491bda 100644
--- a/ext/intl/dateformat/dateformat.stub.php
+++ b/ext/intl/dateformat/dateformat.stub.php
@@ -136,7 +136,7 @@ public function getTimeZone(): IntlTimeZone|false {}
      * @tentative-return-type
      * @alias datefmt_set_timezone
      */
-    public function setTimeZone($timezone): ?bool {} // TODO return true on success
+    public function setTimeZone($timezone): bool {}
 
     /**
      * @tentative-return-type
diff --git a/ext/intl/dateformat/dateformat_arginfo.h b/ext/intl/dateformat/dateformat_arginfo.h
index 6026077c1ac23..6391c5839e09f 100644
--- a/ext/intl/dateformat/dateformat_arginfo.h
+++ b/ext/intl/dateformat/dateformat_arginfo.h
@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: cefec46af242e6372a923dea0e1d2cf22da7ef3e */
+ * Stub hash: c3aabab98e4864276f6cb0afb2e3fefad0386481 */
 
 ZEND_BEGIN_ARG_INFO_EX(arginfo_class_IntlDateFormatter___construct, 0, 0, 1)
 	ZEND_ARG_TYPE_INFO(0, locale, IS_STRING, 1)
@@ -39,7 +39,7 @@ ZEND_END_ARG_INFO()
 ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_OBJ_TYPE_MASK_EX(arginfo_class_IntlDateFormatter_getTimeZone, 0, 0, IntlTimeZone, MAY_BE_FALSE)
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_class_IntlDateFormatter_setTimeZone, 0, 1, _IS_BOOL, 1)
+ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_class_IntlDateFormatter_setTimeZone, 0, 1, _IS_BOOL, 0)
 	ZEND_ARG_INFO(0, timezone)
 ZEND_END_ARG_INFO()
 
diff --git a/ext/intl/dateformat/dateformat_attrcpp.cpp b/ext/intl/dateformat/dateformat_attrcpp.cpp
index a9b9a3d8f5079..e34c331800622 100644
--- a/ext/intl/dateformat/dateformat_attrcpp.cpp
+++ b/ext/intl/dateformat/dateformat_attrcpp.cpp
@@ -101,6 +101,8 @@ U_CFUNC PHP_FUNCTION(datefmt_set_timezone)
 	}
 
 	fetch_datefmt(dfo)->adoptTimeZone(timezone);
+
+	RETURN_TRUE;
 }
 
 /* {{{ Get formatter calendar type. */
diff --git a/ext/intl/php_intl.stub.php b/ext/intl/php_intl.stub.php
index c21ad58fa092e..8980a807919b9 100644
--- a/ext/intl/php_intl.stub.php
+++ b/ext/intl/php_intl.stub.php
@@ -351,7 +351,7 @@ function datefmt_get_calendar_object(IntlDateFormatter $formatter): IntlCalendar
 function datefmt_get_timezone(IntlDateFormatter $formatter): IntlTimeZone|false {}
 
 /** @param IntlTimeZone|DateTimeZone|string|null $timezone */
-function datefmt_set_timezone(IntlDateFormatter $formatter, $timezone): ?bool {}
+function datefmt_set_timezone(IntlDateFormatter $formatter, $timezone): bool {}
 
 function datefmt_set_pattern(IntlDateFormatter $formatter, string $pattern): bool {}
 
diff --git a/ext/intl/php_intl_arginfo.h b/ext/intl/php_intl_arginfo.h
index b715413989145..8f2903315a386 100644
--- a/ext/intl/php_intl_arginfo.h
+++ b/ext/intl/php_intl_arginfo.h
@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 7008d442eba36e2bc468cc4a7a30eb859d10c07d */
+ * Stub hash: 136c14d9162548cd7211985ce9a5d767a90a0b99 */
 
 ZEND_BEGIN_ARG_WITH_RETURN_OBJ_INFO_EX(arginfo_intlcal_create_instance, 0, 0, IntlCalendar, 1)
 	ZEND_ARG_INFO_WITH_DEFAULT_VALUE(0, timezone, "null")
@@ -310,7 +310,7 @@ ZEND_BEGIN_ARG_WITH_RETURN_OBJ_TYPE_MASK_EX(arginfo_datefmt_get_timezone, 0, 1,
 	ZEND_ARG_OBJ_INFO(0, formatter, IntlDateFormatter, 0)
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_datefmt_set_timezone, 0, 2, _IS_BOOL, 1)
+ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_datefmt_set_timezone, 0, 2, _IS_BOOL, 0)
 	ZEND_ARG_OBJ_INFO(0, formatter, IntlDateFormatter, 0)
 	ZEND_ARG_INFO(0, timezone)
 ZEND_END_ARG_INFO()
diff --git a/ext/intl/tests/dateformat_set_timezone_id2.phpt b/ext/intl/tests/dateformat_set_timezone_id2.phpt
index 6c21df6feed56..fa9e68bd86764 100644
--- a/ext/intl/tests/dateformat_set_timezone_id2.phpt
+++ b/ext/intl/tests/dateformat_set_timezone_id2.phpt
@@ -37,7 +37,7 @@ function ut_main()
 
         $res_str .= "-----------";
         $res_str .= "\nTrying to set timezone_id= $timezone_id_entry";
-        ut_datefmt_set_timezone_id( $fmt , $timezone_id_entry );
+        if (ut_datefmt_set_timezone_id( $fmt , $timezone_id_entry ) !== true) die("ut_datefmt_set_timezone_id failed");
         $timezone_id = ut_datefmt_get_timezone_id( $fmt );
         $res_str .= "\nAfter call to set_timezone_id :  timezone_id= $timezone_id";
         $formatted = ut_datefmt_format( $fmt, 0);
diff --git a/ext/intl/tests/dateformat_set_timezone_id3.phpt b/ext/intl/tests/dateformat_set_timezone_id3.phpt
index a4952eb5a3dcb..ec14db3e60623 100644
--- a/ext/intl/tests/dateformat_set_timezone_id3.phpt
+++ b/ext/intl/tests/dateformat_set_timezone_id3.phpt
@@ -20,10 +20,10 @@ ini_set("intl.error_level", E_WARNING);
 function ut_main()
 {
     $timezone_id_arr = array (
-        'America/New_York',
-        'America/Los_Angeles',
-        'America/Chicago',
-        'CN'
+        'America/New_York' => true,
+        'America/Los_Angeles' => true,
+        'America/Chicago' => true,
+        'CN' => false
     );
     $timestamp_entry = 0;
 
@@ -33,12 +33,12 @@ function ut_main()
     $timezone_id = ut_datefmt_get_timezone_id( $fmt );
     $res_str .= "\nAfter creation of the dateformatter :  timezone_id= $timezone_id\n";
 
-    foreach( $timezone_id_arr as $timezone_id_entry )
+    foreach( $timezone_id_arr as $timezone_id_entry => $result )
     {
 
         $res_str .= "-----------";
         $res_str .= "\nTrying to set timezone_id= $timezone_id_entry";
-        ut_datefmt_set_timezone_id( $fmt , $timezone_id_entry );
+        if (ut_datefmt_set_timezone_id( $fmt , $timezone_id_entry ) !== $result) die("ut_datefmt_set_timezone_id failed");
         $timezone_id = ut_datefmt_get_timezone_id( $fmt );
         $res_str .= "\nAfter call to set_timezone_id :  timezone_id= $timezone_id";
         $formatted = ut_datefmt_format( $fmt, 0);
diff --git a/ext/intl/tests/dateformat_set_timezone_id_icu72-1.phpt b/ext/intl/tests/dateformat_set_timezone_id_icu72-1.phpt
index aedf886da2dd0..79953ab26b465 100644
--- a/ext/intl/tests/dateformat_set_timezone_id_icu72-1.phpt
+++ b/ext/intl/tests/dateformat_set_timezone_id_icu72-1.phpt
@@ -19,10 +19,10 @@ ini_set("intl.error_level", E_WARNING);
 function ut_main()
 {
     $timezone_id_arr = array (
-        'America/New_York',
-        'America/Los_Angeles',
-        'America/Chicago',
-        'CN'
+        'America/New_York' => true,
+        'America/Los_Angeles' => true,
+        'America/Chicago' => true,
+        'CN' => false
     );
     $timestamp_entry = 0;
 
@@ -32,12 +32,12 @@ function ut_main()
     $timezone_id = ut_datefmt_get_timezone_id( $fmt );
     $res_str .= "\nAfter creation of the dateformatter :  timezone_id= $timezone_id\n";
 
-    foreach( $timezone_id_arr as $timezone_id_entry )
+    foreach( $timezone_id_arr as $timezone_id_entry => $result )
     {
 
         $res_str .= "-----------";
         $res_str .= "\nTrying to set timezone_id= $timezone_id_entry";
-        ut_datefmt_set_timezone_id( $fmt , $timezone_id_entry );
+        if (ut_datefmt_set_timezone_id( $fmt , $timezone_id_entry ) !== $result) die("ut_datefmt_set_timezone_id failed");
         $timezone_id = ut_datefmt_get_timezone_id( $fmt );
         $res_str .= "\nAfter call to set_timezone_id :  timezone_id= $timezone_id";
         $formatted = ut_datefmt_format( $fmt, 0);