diff --git a/ext/session/mod_files.c b/ext/session/mod_files.c
index 87bcb7e3690fc..072fed351dbff 100644
--- a/ext/session/mod_files.c
+++ b/ext/session/mod_files.c
@@ -451,7 +451,7 @@ PS_CLOSE_FUNC(files)
 
 	zend_string_release_ex(data->basedir, /* persistent */ false);
 	efree(data);
-	PS_SET_MOD_DATA(NULL);
+	PS_SET_MOD_DATA(data);
 
 	return SUCCESS;
 }
diff --git a/ext/session/tests/sessionhandler_validateid_return_type.phpt b/ext/session/tests/sessionhandler_validateid_return_type.phpt
new file mode 100644
index 0000000000000..a100694588206
--- /dev/null
+++ b/ext/session/tests/sessionhandler_validateid_return_type.phpt
@@ -0,0 +1,35 @@
+--TEST--
+SessionHandler::validateId must return bool
+--INI--
+session.use_strict_mode=1
+--EXTENSIONS--
+session
+--SKIPIF--
+<?php include('skipif.inc'); ?>
+--FILE--
+<?php
+class MySession extends SessionHandler {
+    public function validateId($key) {
+        return null;
+    }
+}
+
+$handler = new MySession();
+
+try {
+    session_set_save_handler($handler);
+    session_start();
+} catch (TypeError $e) {
+    echo $e->getMessage(), "\n";
+}
+
+session_write_close();
+
+try {
+    session_start();
+} catch (Throwable $e) {
+    echo $e->getMessage(), "\n";
+}
+?>
+--EXPECTF--
+Session id must be a string