diff --git a/ext/date/php_date.c b/ext/date/php_date.c
index f4cbe3765e4..0fae1380674 100644
--- a/ext/date/php_date.c
+++ b/ext/date/php_date.c
@@ -4270,7 +4270,8 @@ static bool date_interval_initialize(timelib_rel_time **rt, /*const*/ char *form
 	return retval;
 } /* }}} */
 
-static int date_interval_compare_objects(zval *o1, zval *o2) {
+static int date_interval_compare_objects(zval *o1, zval *o2)
+{
 	ZEND_COMPARE_OBJECTS_FALLBACK(o1, o2);
 	/* There is no well defined way to compare intervals like P1M and P30D, which may compare
 	 * smaller, equal or greater depending on the point in time at which the interval starts. As
@@ -4843,7 +4844,8 @@ static bool date_period_initialize(timelib_time **st, timelib_time **et, timelib
 	return retval;
 } /* }}} */
 
-static bool date_period_init_iso8601_string(php_period_obj *dpobj, char *isostr, size_t isostr_len, zend_long options, zend_long *recurrences) {
+static bool date_period_init_iso8601_string(php_period_obj *dpobj, zend_class_entry* base_ce, char *isostr, size_t isostr_len, zend_long options, zend_long *recurrences)
+{
 	if (!date_period_initialize(&(dpobj->start), &(dpobj->end), &(dpobj->interval), recurrences, isostr, isostr_len)) {
 		return false;
 	}
@@ -4873,12 +4875,13 @@ static bool date_period_init_iso8601_string(php_period_obj *dpobj, char *isostr,
 	if (dpobj->end) {
 		timelib_update_ts(dpobj->end, NULL);
 	}
-	dpobj->start_ce = date_ce_date;
+	dpobj->start_ce = base_ce;
 
 	return true;
 }
 
-static bool date_period_init_finish(php_period_obj *dpobj, zend_long options, zend_long recurrences) {
+static bool date_period_init_finish(php_period_obj *dpobj, zend_long options, zend_long recurrences)
+{
 	if (dpobj->end == NULL && recurrences < 1) {
 		zend_string *func = get_active_function_or_method_name();
 		zend_throw_exception_ex(date_ce_date_malformed_period_string_exception, 0, "%s(): Recurrence count must be greater than 0", ZSTR_VAL(func));
@@ -4916,7 +4919,7 @@ PHP_METHOD(DatePeriod, createFromISO8601String)
 
 	dpobj->current = NULL;
 
-	if (!date_period_init_iso8601_string(dpobj, isostr, isostr_len, options, &recurrences)) {
+	if (!date_period_init_iso8601_string(dpobj, date_ce_immutable, isostr, isostr_len, options, &recurrences)) {
 		RETURN_THROWS();
 	}
 
@@ -4949,7 +4952,7 @@ PHP_METHOD(DatePeriod, __construct)
 	dpobj->current = NULL;
 
 	if (isostr) {
-		if (!date_period_init_iso8601_string(dpobj, isostr, isostr_len, options, &recurrences)) {
+		if (!date_period_init_iso8601_string(dpobj, date_ce_date, isostr, isostr_len, options, &recurrences)) {
 			RETURN_THROWS();
 		}
 	} else {
diff --git a/ext/date/tests/DatePeriod_createFromISO8601String_static_return.phpt b/ext/date/tests/DatePeriod_createFromISO8601String_static_return.phpt
index 60b58e79cd3..f8b1e1cffe4 100644
--- a/ext/date/tests/DatePeriod_createFromISO8601String_static_return.phpt
+++ b/ext/date/tests/DatePeriod_createFromISO8601String_static_return.phpt
@@ -23,7 +23,7 @@ try {
 --EXPECT--
 object(MyDatePeriod)#1 (7) {
   ["start"]=>
-  object(DateTime)#2 (3) {
+  object(DateTimeImmutable)#2 (3) {
     ["date"]=>
     string(26) "2012-07-01 00:00:00.000000"
     ["timezone_type"]=>
diff --git a/ext/date/tests/DatePeriod_serialize-001.phpt b/ext/date/tests/DatePeriod_serialize-001.phpt
index 8d7569b58dc..c30a4eb0ef1 100644
--- a/ext/date/tests/DatePeriod_serialize-001.phpt
+++ b/ext/date/tests/DatePeriod_serialize-001.phpt
@@ -24,7 +24,7 @@ var_dump($d->__serialize());
 Original object:
 object(DatePeriod)#%d (%d) {
   ["start"]=>
-  object(DateTime)#%d (%d) {
+  object(DateTimeImmutable)#%d (%d) {
     ["date"]=>
     string(26) "2012-07-01 00:00:00.000000"
     ["timezone_type"]=>
@@ -69,13 +69,13 @@ object(DatePeriod)#%d (%d) {
 
 
 Serialised object:
-string(%d) "O:10:"DatePeriod":7:{s:5:"start";O:8:"DateTime":3:{s:4:"date";s:26:"2012-07-01 00:00:00.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}s:7:"current";N;s:3:"end";N;s:8:"interval";O:12:"DateInterval":10:{s:1:"y";i:0;s:1:"m";i:0;s:1:"d";i:7;s:1:"h";i:0;s:1:"i";i:0;s:1:"s";i:0;s:1:"f";d:0;s:6:"invert";i:0;s:4:"days";b:0;s:11:"from_string";b:0;}s:11:"recurrences";i:5;s:18:"include_start_date";b:1;s:16:"include_end_date";b:0;}"
+string(%d) "O:10:"DatePeriod":7:{s:5:"start";O:17:"DateTimeImmutable":3:{s:4:"date";s:26:"2012-07-01 00:00:00.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}s:7:"current";N;s:3:"end";N;s:8:"interval";O:12:"DateInterval":10:{s:1:"y";i:0;s:1:"m";i:0;s:1:"d";i:7;s:1:"h";i:0;s:1:"i";i:0;s:1:"s";i:0;s:1:"f";d:0;s:6:"invert";i:0;s:4:"days";b:0;s:11:"from_string";b:0;}s:11:"recurrences";i:5;s:18:"include_start_date";b:1;s:16:"include_end_date";b:0;}"
 
 
 Unserialised object:
 object(DatePeriod)#%d (%d) {
   ["start"]=>
-  object(DateTime)#%d (%d) {
+  object(DateTimeImmutable)#%d (%d) {
     ["date"]=>
     string(26) "2012-07-01 00:00:00.000000"
     ["timezone_type"]=>
@@ -122,7 +122,7 @@ object(DatePeriod)#%d (%d) {
 Calling __serialize manually:
 array(%d) {
   ["start"]=>
-  object(DateTime)#%d (%d) {
+  object(DateTimeImmutable)#%d (%d) {
     ["date"]=>
     string(26) "2012-07-01 00:00:00.000000"
     ["timezone_type"]=>