diff --git a/phpBB/includes/acp/acp_main.php b/phpBB/includes/acp/acp_main.php
index 08ba060207..e738b62207 100644
--- a/phpBB/includes/acp/acp_main.php
+++ b/phpBB/includes/acp/acp_main.php
@@ -493,7 +493,7 @@ class acp_main
 
 		$start_date = $user->format_date($config['board_startdate']);
 
-		$boarddays = (time() - $config['board_startdate']) / 86400;
+		$boarddays = (time() - (int) $config['board_startdate']) / 86400;
 
 		$posts_per_day = sprintf('%.2f', $total_posts / $boarddays);
 		$topics_per_day = sprintf('%.2f', $total_topics / $boarddays);