diff --git a/NEWS b/NEWS
index c4e05157546..c03d16720cc 100644
--- a/NEWS
+++ b/NEWS
@@ -14,6 +14,7 @@ PHP                                                                        NEWS
 
 - Date:
   . Fixed bug #70153 (\DateInterval incorrectly unserialized). (Maksim Iakunin)
+  . Fixed bug #78751 (Serialising DatePeriod converts DateTimeImmutable). (cmb)
 
 - Iconv:
   . Fixed bug #78642 (Wrong libiconv version displayed). (gedas at martynas,
diff --git a/ext/date/php_date.c b/ext/date/php_date.c
index 49df94f5925..00656a41f97 100644
--- a/ext/date/php_date.c
+++ b/ext/date/php_date.c
@@ -5168,7 +5168,7 @@ static HashTable *date_object_get_properties_period(zval *object) /* {{{ */
 
 	if (period_obj->start) {
 		php_date_obj *date_obj;
-		object_init_ex(&zv, date_ce_date);
+		object_init_ex(&zv, period_obj->start_ce);
 		date_obj = Z_PHPDATE_P(&zv);
 		date_obj->time = timelib_time_clone(period_obj->start);
 	} else {
@@ -5178,7 +5178,7 @@ static HashTable *date_object_get_properties_period(zval *object) /* {{{ */
 
 	if (period_obj->current) {
 		php_date_obj *date_obj;
-		object_init_ex(&zv, date_ce_date);
+		object_init_ex(&zv, period_obj->start_ce);
 		date_obj = Z_PHPDATE_P(&zv);
 		date_obj->time = timelib_time_clone(period_obj->current);
 	} else {
@@ -5188,7 +5188,7 @@ static HashTable *date_object_get_properties_period(zval *object) /* {{{ */
 
 	if (period_obj->end) {
 		php_date_obj *date_obj;
-		object_init_ex(&zv, date_ce_date);
+		object_init_ex(&zv, period_obj->start_ce);
 		date_obj = Z_PHPDATE_P(&zv);
 		date_obj->time = timelib_time_clone(period_obj->end);
 	} else {
@@ -5225,7 +5225,7 @@ static int php_date_period_initialize_from_hash(php_period_obj *period_obj, Hash
 
 	ht_entry = zend_hash_str_find(myht, "start", sizeof("start")-1);
 	if (ht_entry) {
-		if (Z_TYPE_P(ht_entry) == IS_OBJECT && Z_OBJCE_P(ht_entry) == date_ce_date) {
+		if (Z_TYPE_P(ht_entry) == IS_OBJECT && instanceof_function(Z_OBJCE_P(ht_entry), date_ce_interface)) {
 			php_date_obj *date_obj;
 			date_obj = Z_PHPDATE_P(ht_entry);
 			period_obj->start = timelib_time_clone(date_obj->time);
@@ -5239,7 +5239,7 @@ static int php_date_period_initialize_from_hash(php_period_obj *period_obj, Hash
 
 	ht_entry = zend_hash_str_find(myht, "end", sizeof("end")-1);
 	if (ht_entry) {
-		if (Z_TYPE_P(ht_entry) == IS_OBJECT && Z_OBJCE_P(ht_entry) == date_ce_date) {
+		if (Z_TYPE_P(ht_entry) == IS_OBJECT && instanceof_function(Z_OBJCE_P(ht_entry), date_ce_interface)) {
 			php_date_obj *date_obj;
 			date_obj = Z_PHPDATE_P(ht_entry);
 			period_obj->end = timelib_time_clone(date_obj->time);
@@ -5252,7 +5252,7 @@ static int php_date_period_initialize_from_hash(php_period_obj *period_obj, Hash
 
 	ht_entry = zend_hash_str_find(myht, "current", sizeof("current")-1);
 	if (ht_entry) {
-		if (Z_TYPE_P(ht_entry) == IS_OBJECT && Z_OBJCE_P(ht_entry) == date_ce_date) {
+		if (Z_TYPE_P(ht_entry) == IS_OBJECT && instanceof_function(Z_OBJCE_P(ht_entry), date_ce_interface)) {
 			php_date_obj *date_obj;
 			date_obj = Z_PHPDATE_P(ht_entry);
 			period_obj->current = timelib_time_clone(date_obj->time);
diff --git a/ext/date/tests/bug78751.phpt b/ext/date/tests/bug78751.phpt
new file mode 100644
index 00000000000..6021b9f6aec
--- /dev/null
+++ b/ext/date/tests/bug78751.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Bug #78751 (Serialising DatePeriod converts DateTimeImmutable)
+--FILE--
+<?php
+$oDay = new DateTimeImmutable('2019-10-25');
+$oDateInterval = DateInterval::createFromDateString('1 day');
+$oDays = new DatePeriod($oDay, $oDateInterval, $oDay->modify('+1 day'));
+$oDays = unserialize(serialize($oDays));
+var_dump(
+    $oDays->start instanceof DateTimeImmutable,
+    $oDays->end instanceof DateTimeImmutable
+);
+?>
+--EXPECT--
+bool(true)
+bool(true)