diff --git a/lib/SimpleSAML/Session.php b/lib/SimpleSAML/Session.php
index 2abb45c96ef52b08cb247ebcb67756ae44032e49..30c8cdf7b9a62d5d1c6b908c4c34e3a0e556dd62 100644
--- a/lib/SimpleSAML/Session.php
+++ b/lib/SimpleSAML/Session.php
@@ -856,7 +856,7 @@ class Session implements \Serializable
      * @param string   $type The type of the data. This is checked when retrieving data from the store.
      * @param string   $id The identifier of the data.
      * @param mixed    $data The data.
-     * @param int|null $timeout The number of seconds this data should be stored after its last access.
+     * @param int|string|null $timeout The number of seconds this data should be stored after its last access.
      * This parameter is optional. The default value is set in 'session.datastore.timeout',
      * and the default is 4 hours.
      *