diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index 14a590ad..65cc153a 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -859,7 +859,7 @@ $("#rcmfd_new_category").keypress(function(event) {
                 'calendar_default_calendar'     => rcube_utils::get_input_value('_default_calendar', rcube_utils::INPUT_POST),
                 'calendar_date_format'          => null,  // clear previously saved values
                 'calendar_time_format'          => null,
-                'calendar_contact_birthdays'      => !empty(rcube_utils::get_input_value('_contact_birthdays', rcube_utils::INPUT_POST)),
+                'calendar_contact_birthdays'      => (bool) rcube_utils::get_input_value('_contact_birthdays', rcube_utils::INPUT_POST),
                 'calendar_birthday_adressbooks'   => (array) rcube_utils::get_input_value('_birthday_adressbooks', rcube_utils::INPUT_POST),
                 'calendar_birthdays_alarm_type'   => rcube_utils::get_input_value('_birthdays_alarm_type', rcube_utils::INPUT_POST),
                 'calendar_birthdays_alarm_offset' => $birthdays_alarm_value ?: null,
diff --git a/plugins/calendar/drivers/kolab/kolab_driver.php b/plugins/calendar/drivers/kolab/kolab_driver.php
index 0ab811a5..1253c773 100644
--- a/plugins/calendar/drivers/kolab/kolab_driver.php
+++ b/plugins/calendar/drivers/kolab/kolab_driver.php
@@ -854,7 +854,7 @@ class kolab_driver extends calendar_driver
             }
 
             // removing an exception instance
-            if ((!empty($event['recurrence_id']) || !empty($event['isexception'])) && !empty(($master['exceptions']))) {
+            if ((!empty($event['recurrence_id']) || !empty($event['isexception'])) && !empty($master['exceptions'])) {
                 foreach ($master['exceptions'] as $i => $exception) {
                     if ($exception['_instance'] == $event['_instance']) {
                         unset($master['exceptions'][$i]);