diff --git a/add_form.php b/add_form.php
index 6cec532..4026324 100644
--- a/add_form.php
+++ b/add_form.php
@@ -158,7 +158,7 @@ class mod_attendance_add_form extends moodleform {
     public function validation($data, $files) {
         $errors = parent::validation($data, $files);
 
-        if ($data['sessiondate'] != 0 && $data['sessionenddate'] != 0 && $data['sessionenddate'] < $data['sessiondate']) {
+        if (!empty($data['addmultiply']) && $data['sessiondate'] != 0 && $data['sessionenddate'] != 0 && $data['sessionenddate'] < $data['sessiondate']) {
             $errors['sessionenddate'] = get_string('invalidsessionenddate', 'attendance');
         }