diff --git a/PVE/AccessControl.pm b/PVE/AccessControl.pm
index 5de060d..fff2df2 100644
--- a/PVE/AccessControl.pm
+++ b/PVE/AccessControl.pm
@@ -283,7 +283,7 @@ sub verify_ticket {
 	return undef if !$rsa_pub;
 
 	my ($min, $max) = $get_ticket_age_range->($now, $rsa_mtime, $old);
-	return undef if !$min;
+	return undef if !defined($min);
 
 	return PVE::Ticket::verify_rsa_ticket(
 	    $rsa_pub, 'PVE', $ticket, undef, $min, $max, 1);