diff --git a/htdocs/core/lib/date.lib.php b/htdocs/core/lib/date.lib.php
index e61788f3f04..0bb10e69b8a 100644
--- a/htdocs/core/lib/date.lib.php
+++ b/htdocs/core/lib/date.lib.php
@@ -124,7 +124,7 @@ function getServerTimeZoneInt($refgmtdate = 'now')
  */
 function dol_time_plus_duree($time, $duration_value, $duration_unit, $ruleforendofmonth = 0)
 {
-	if (empty($duration_value)) {
+	if (!isDolTms($duration_value)) {
 		return $time;
 	}
 	if ($duration_unit == 's') {