diff --git a/service/posting.php b/service/posting.php
index 06dd782..14db1fb 100644
--- a/service/posting.php
+++ b/service/posting.php
@@ -109,7 +109,7 @@ public function get_template_vars(int $forum_id, array $topic_data):array
 			'maxDuration'	=> $this->store->get_max_duration_days(),
 			'dateFormat'	=> $this->store->get_date_format(),
 			'firstDay'		=> $this->store->get_first_day(),
-			'refTime'		=> (int) $topic_data['topic_time'] ?? time(),
+			'refTime'		=> isset($topic_data['topic_time']) ? (int) $topic_data['topic_time'] : time(),
 		];
 
 		$start_date = $start_jd ? $this->jd_to_atom_date($start_jd) : '';