diff --git a/lib/CalDAV/Backend/PDO.php b/lib/CalDAV/Backend/PDO.php
index 1357aa2ecb..acda1c9cbd 100644
--- a/lib/CalDAV/Backend/PDO.php
+++ b/lib/CalDAV/Backend/PDO.php
@@ -790,7 +790,7 @@ public function calendarQuery($calendarId, array $filters)
                 // If start time OR the end time is not specified, we can do a
                 // 100% accurate mysql query.
                 if (!$filters['prop-filters'] && !$filters['comp-filters'][0]['comp-filters'] && !$filters['comp-filters'][0]['prop-filters'] && $timeRange) {
-                    if (!$timeRange['start'] || !$timeRange['end']) {
+                    if ((array_key_exists('start', $timeRange) && !$timeRange['start']) || (array_key_exists('end', $timeRange) && !$timeRange['end'])) {
                         $requirePostFilter = false;
                     }
                 }
@@ -812,11 +812,11 @@ public function calendarQuery($calendarId, array $filters)
             $values['componenttype'] = $componentType;
         }
 
-        if ($timeRange && $timeRange['start']) {
+        if ($timeRange && array_key_exists('start', $timeRange) && $timeRange['start']) {
             $query .= ' AND lastoccurence > :startdate';
             $values['startdate'] = $timeRange['start']->getTimeStamp();
         }
-        if ($timeRange && $timeRange['end']) {
+        if ($timeRange && array_key_exists('end', $timeRange) && $timeRange['end']) {
             $query .= ' AND firstoccurence < :enddate';
             $values['enddate'] = $timeRange['end']->getTimeStamp();
         }