diff --git a/ext/session/session.c b/ext/session/session.c
index ef97f856499f..d3b4146a1e5f 100644
--- a/ext/session/session.c
+++ b/ext/session/session.c
@@ -526,6 +526,7 @@ static void php_session_save_current_state(bool write)
 				/* Not being able to encode the session data means there is some kind of issue that prevents a write
 				 * (e.g. a key containing the '|' character with the default serialization) */
 				if (UNEXPECTED(val == NULL)) {
+					PS(mod)->s_close(&PS(mod_data));
 					return;
 				}
 
diff --git a/ext/session/tests/session_write_close_encode_failure.phpt b/ext/session/tests/session_write_close_encode_failure.phpt
new file mode 100644
index 000000000000..1c562f401df2
--- /dev/null
+++ b/ext/session/tests/session_write_close_encode_failure.phpt
@@ -0,0 +1,76 @@
+--TEST--
+session_write_close() closes the save handler when encoding the session data fails
+--EXTENSIONS--
+session
+--SKIPIF--
+<?php include('skipif.inc'); ?>
+--INI--
+session.use_cookies=0
+session.cache_limiter=
+session.serialize_handler=php
+session.save_handler=files
+--FILE--
+<?php
+ob_start();
+$dir = __DIR__ . '/session_write_close_encode_failure';
+@mkdir($dir);
+session_save_path($dir);
+session_start();
+$file = $dir . '/sess_' . session_id();
+$_SESSION['bad|key'] = 'value';
+var_dump(session_write_close());
+
+$fp = fopen($file, 'r');
+var_dump(flock($fp, LOCK_EX | LOCK_NB));
+fclose($fp);
+
+session_start();
+$file = $dir . '/sess_' . session_id();
+$_SESSION['closure'] = function () {};
+$_SESSION['bad|key'] = 'value';
+try {
+    session_write_close();
+} catch (Exception $e) {
+    echo $e::class, ": ", $e->getMessage(), PHP_EOL;
+}
+
+$fp = fopen($file, 'r');
+var_dump(flock($fp, LOCK_EX | LOCK_NB));
+fclose($fp);
+
+class Handler extends SessionHandler
+{
+    public function close(): bool
+    {
+        echo "close\n";
+        return parent::close();
+    }
+}
+
+session_set_save_handler(new Handler());
+session_start();
+$_SESSION['bad|key'] = 'value';
+var_dump(session_write_close());
+echo "done\n";
+?>
+--CLEAN--
+<?php
+$dir = __DIR__ . '/session_write_close_encode_failure';
+foreach (glob($dir . '/sess_*') as $file) {
+    unlink($file);
+}
+@rmdir($dir);
+?>
+--EXPECTF--
+Warning: session_write_close(): Failed to write session data. Data contains invalid key "bad|key" in %s on line %d
+bool(true)
+bool(true)
+
+Warning: session_write_close(): Failed to write session data. Data contains invalid key "bad|key" in %s on line %d
+Exception: Serialization of 'Closure' is not allowed
+bool(true)
+
+Warning: session_write_close(): Failed to write session data. Data contains invalid key "bad|key" in %s on line %d
+close
+bool(true)
+done