diff --git a/add_form.php b/add_form.php
index dabaeb1..51bffba 100644
--- a/add_form.php
+++ b/add_form.php
@@ -161,6 +161,12 @@ class mod_attendance_add_form extends moodleform {
         if ($data['sessiontype'] == attendance::SESSION_GROUP and empty($data['groups'])) {
             $errors['groups'] = get_string('errorgroupsnotselected', 'attendance');
         }
+
+        $addmulti = isset($data['addmultiply'])? (int)$data['addmultiply'] : 0;
+        if (($addmulti != 0) && (!array_key_exists('sdays',$data) || empty($data['sdays']))) {
+            $data['sdays']= array();
+            $errors['sdays'] = get_string('required', 'attendance');
+        }
         return $errors;
     }
 
diff --git a/lang/en/attendance.php b/lang/en/attendance.php
index 9d4387a..f79b88a 100755
--- a/lang/en/attendance.php
+++ b/lang/en/attendance.php
@@ -153,6 +153,7 @@ $string['pluginname'] = 'Attendance';
 $string['pluginadministration'] = 'Attendance administration';
 $string['remarks'] = 'Remarks';
 $string['report'] = 'Report';
+$string['required'] = 'Required*';
 $string['resetdescription'] = 'Remember that deleting attendance data will erase information from database. You can just hide older sessions having changed start date of course!';
 $string['resetstatuses'] = 'Reset statuses to default';
 $string['restoredefaults'] = 'Restore defaults';