diff --git a/htdocs/cron/card.php b/htdocs/cron/card.php
index 0a68ca211b9e3b10ce38d551f9b32af818fd4813..79306fb1d65fe343ae129df21950c8bbdaa60c61 100644
--- a/htdocs/cron/card.php
+++ b/htdocs/cron/card.php
@@ -354,7 +354,7 @@ if (($action=="create") || ($action=="edit"))
 	print $langs->trans('CronEvery')."</td>";
 	print "<td><select name=\"nbfrequency\">";
 	for($i=1; $i<=60; $i++){
-		if(($object->frequency/$object->unitfrequency) == $i){
+		if(!is_null($object->unitfrequency) && ($object->frequency/$object->unitfrequency) == $i){
 			print "<option value='".$i."' selected='selected'>".$i."</option>";
 		}
 		else{