diff --git a/NEWS b/NEWS
index 3b9ad03e11e..bc468c50c77 100644
--- a/NEWS
+++ b/NEWS
@@ -6,6 +6,10 @@ PHP                                                                        NEWS
   . Fixed bug #81518 (Header injection via default_mimetype / default_charset).
     (cmb)
 
+- Date:
+  . Fixed bug #81500 (Interval serialization regression since 7.3.14 / 7.4.2).
+    (cmb)
+
 14 Oct 2021, PHP 8.1.0RC4
 
 - CLI:
diff --git a/ext/date/php_date.c b/ext/date/php_date.c
index e2943e6f708..cf4a11b8a22 100644
--- a/ext/date/php_date.c
+++ b/ext/date/php_date.c
@@ -3850,7 +3850,7 @@ static zval *date_interval_write_property(zend_object *object, zend_string *name
 		SET_VALUE_FROM_STRUCT(i, "i");
 		SET_VALUE_FROM_STRUCT(s, "s");
 		if (zend_string_equals_literal(name, "f")) {
-			obj->diff->us = zval_get_double(value) * 1000000;
+			obj->diff->us = zend_dval_to_lval(zval_get_double(value) * 1000000.0);
 			break;
 		}
 		SET_VALUE_FROM_STRUCT(invert, "invert");
@@ -3968,12 +3968,8 @@ static int php_date_interval_initialize_from_hash(zval **return_value, php_inter
 	PHP_DATE_INTERVAL_READ_PROPERTY("s", s, timelib_sll, -1)
 	{
 		zval *z_arg = zend_hash_str_find(myht, "f", sizeof("f") - 1);
-		(*intobj)->diff->us = -1000000;
 		if (z_arg) {
-			double val = zval_get_double(z_arg) * 1000000;
-			if (val >= 0 && val < 1000000) {
-				(*intobj)->diff->us = val;
-			}
+			(*intobj)->diff->us = zend_dval_to_lval(zval_get_double(z_arg) * 1000000.0);
 		}
 	}
 	PHP_DATE_INTERVAL_READ_PROPERTY("weekday", weekday, int, -1)
diff --git a/ext/date/tests/bug53437_var3.phpt b/ext/date/tests/bug53437_var3.phpt
index 44e6a80c89e..eb043398e2d 100644
--- a/ext/date/tests/bug53437_var3.phpt
+++ b/ext/date/tests/bug53437_var3.phpt
@@ -43,5 +43,5 @@ object(DateInterval)#%d (16) {
   ["have_special_relative"]=>
   int(0)
   ["f"]=>
-  float(-1)
+  float(0)
 }
diff --git a/ext/date/tests/bug53437_var5.phpt b/ext/date/tests/bug53437_var5.phpt
index baffbb484ad..55bba9ed59d 100644
--- a/ext/date/tests/bug53437_var5.phpt
+++ b/ext/date/tests/bug53437_var5.phpt
@@ -43,5 +43,5 @@ object(DateInterval)#%d (16) {
   ["have_special_relative"]=>
   int(0)
   ["f"]=>
-  float(-1)
+  float(0)
 }
diff --git a/ext/date/tests/bug73091.phpt b/ext/date/tests/bug73091.phpt
index 14f161afe74..918170d823f 100644
--- a/ext/date/tests/bug73091.phpt
+++ b/ext/date/tests/bug73091.phpt
@@ -28,7 +28,7 @@ object(DateInterval)#%d (16) {
   ["s"]=>
   int(-1)
   ["f"]=>
-  float(-1)
+  float(0)
   ["weekday"]=>
   int(-1)
   ["weekday_behavior"]=>
diff --git a/ext/date/tests/bug79015.phpt b/ext/date/tests/bug79015.phpt
index 5ebb13832b7..9d752dee722 100644
--- a/ext/date/tests/bug79015.phpt
+++ b/ext/date/tests/bug79015.phpt
@@ -20,7 +20,7 @@ object(DateInterval)#%d (16) {
   ["s"]=>
   int(0)
   ["f"]=>
-  float(-1)
+  float(%f)
   ["weekday"]=>
   int(0)
   ["weekday_behavior"]=>
diff --git a/ext/date/tests/bug81500.phpt b/ext/date/tests/bug81500.phpt
new file mode 100644
index 00000000000..0c60c204a34
--- /dev/null
+++ b/ext/date/tests/bug81500.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Bug #81500 (Interval serialization regression since 7.3.14 / 7.4.2)
+--FILE--
+<?php
+$interval = new DateInterval('PT1S');
+$interval->f = -0.000001;
+var_dump($interval->s, $interval->f);
+
+$interval = unserialize(serialize($interval));
+var_dump($interval->s, $interval->f);
+?>
+--EXPECT--
+int(1)
+float(-1.0E-6)
+int(1)
+float(-1.0E-6)
diff --git a/ext/standard/tests/serialize/bug69425.phpt b/ext/standard/tests/serialize/bug69425.phpt
index e080fda7dd5..906c7192fb2 100644
--- a/ext/standard/tests/serialize/bug69425.phpt
+++ b/ext/standard/tests/serialize/bug69425.phpt
@@ -40,7 +40,7 @@ array(2) {
     ["s"]=>
     int(-1)
     ["f"]=>
-    float(-1)
+    float(0)
     ["weekday"]=>
     int(-1)
     ["weekday_behavior"]=>