diff --git a/docs/source/miscellaneous/writing-tests.rst b/docs/source/miscellaneous/writing-tests.rst
index 8c4e0535763c..dae6c1d861ef 100644
--- a/docs/source/miscellaneous/writing-tests.rst
+++ b/docs/source/miscellaneous/writing-tests.rst
@@ -235,7 +235,7 @@ and not in the INI section. This is because of the order in which settings are c
 
    date_default_timezone_set() -> TZ environmental -> INI setting -> System Setting
 
-If a TZ environmental varaibale is found the INI setting will be ignored.
+If a TZ environmental variable is found the INI setting will be ignored.
 
 Tests that run, or only have have matching EXPECT output, on 32bit platforms can use a SKIPIF
 section like:
diff --git a/ext/date/php_date.c b/ext/date/php_date.c
index e462b70d2cff..c811c2493a01 100644
--- a/ext/date/php_date.c
+++ b/ext/date/php_date.c
@@ -5747,7 +5747,7 @@ static bool php_date_period_initialize_from_hash(php_period_obj *period_obj, con
 			php_date_obj *date_obj;
 			date_obj = Z_PHPDATE_P(ht_entry);
 
-			if (!date_obj->time) {
+			if (!date_obj->time || !period_obj->start_ce) {
 				return false;
 			}
 
@@ -5768,7 +5768,7 @@ static bool php_date_period_initialize_from_hash(php_period_obj *period_obj, con
 			php_date_obj *date_obj;
 			date_obj = Z_PHPDATE_P(ht_entry);
 
-			if (!date_obj->time) {
+			if (!date_obj->time || !period_obj->start_ce) {
 				return false;
 			}
 
diff --git a/ext/date/tests/gh20936.phpt b/ext/date/tests/gh20936.phpt
new file mode 100644
index 000000000000..e6a525dd4583
--- /dev/null
+++ b/ext/date/tests/gh20936.phpt
@@ -0,0 +1,14 @@
+--TEST--
+GH-20936 (DatePeriod::__set_state() cannot handle null start)
+--FILE--
+<?php
+$end = new DateTime('2022-07-16', new DateTimeZone('UTC'));
+$interval = new DateInterval('P2D');
+try {
+    DatePeriod::__set_state(['start' => null, 'end' => $end, 'current' => null, 'interval' => $interval, 'recurrences' => 2, 'include_start_date' => false, 'include_end_date' => true]);
+} catch (Throwable $e) {
+    echo $e::class, ": ", $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+Error: Invalid serialization data for DatePeriod object