diff --git a/plugins/calendar/drivers/kolab/kolab_calendar.php b/plugins/calendar/drivers/kolab/kolab_calendar.php
index 19a03e15..9043b4a9 100644
--- a/plugins/calendar/drivers/kolab/kolab_calendar.php
+++ b/plugins/calendar/drivers/kolab/kolab_calendar.php
@@ -251,14 +251,16 @@ class kolab_calendar extends kolab_storage_folder_api
   public function list_events($start, $end, $search = null, $virtual = 1, $query = array(), $filter_query = null)
   {
     // convert to DateTime for comparisons
+    // #5190: make the range a little bit wider
+    // to workaround possible timezone differences
     try {
-      $start = new DateTime('@'.$start);
+      $start = new DateTime('@' . ($start - 12 * 3600));
     }
     catch (Exception $e) {
       $start = new DateTime('@0');
     }
     try {
-      $end = new DateTime('@'.$end);
+      $end = new DateTime('@' . ($end + 12 * 3600));
     }
     catch (Exception $e) {
       $end = new DateTime('today +10 years');
diff --git a/plugins/libkolab/lib/kolab_storage_cache.php b/plugins/libkolab/lib/kolab_storage_cache.php
index 9f4533cc..bcc9ac3f 100644
--- a/plugins/libkolab/lib/kolab_storage_cache.php
+++ b/plugins/libkolab/lib/kolab_storage_cache.php
@@ -50,6 +50,7 @@ class kolab_storage_cache
     protected $order_by = null;
     protected $limit = null;
     protected $error = 0;
+    protected $server_timezone;
 
 
     /**
@@ -84,6 +85,7 @@ class kolab_storage_cache
         $this->enabled = $rcmail->config->get('kolab_cache', false);
         $this->folders_table = $this->db->table_name('kolab_folders');
         $this->cache_refresh = get_offset_sec($rcmail->config->get('kolab_cache_refresh', '12h'));
+        $this->server_timezone = new DateTimeZone(date_default_timezone_get());
 
         if ($this->enabled) {
             // always read folder cache and lock state from DB master
@@ -1145,4 +1147,19 @@ class kolab_storage_cache
         }
     }
 
+    /**
+     * Converts DateTime or unix timestamp into sql date format
+     * using server timezone.
+     */
+    protected function _convert_datetime($datetime)
+    {
+        if (is_object($datetime)) {
+            $dt = clone $datetime;
+            $dt->setTimeZone($this->server_timezone);
+            return $dt->format(self::DB_DATE_FORMAT);
+        }
+        else if ($datetime) {
+            return date(self::DB_DATE_FORMAT, $datetime);
+        }
+    }
 }
diff --git a/plugins/libkolab/lib/kolab_storage_cache_event.php b/plugins/libkolab/lib/kolab_storage_cache_event.php
index e25bd899..ae9c693b 100644
--- a/plugins/libkolab/lib/kolab_storage_cache_event.php
+++ b/plugins/libkolab/lib/kolab_storage_cache_event.php
@@ -34,27 +34,27 @@ class kolab_storage_cache_event extends kolab_storage_cache
     {
         $sql_data = parent::_serialize($object);
 
-        $sql_data['dtstart'] = is_object($object['start']) ? $object['start']->format(self::DB_DATE_FORMAT) : date(self::DB_DATE_FORMAT, $object['start']);
-        $sql_data['dtend']   = is_object($object['end'])   ? $object['end']->format(self::DB_DATE_FORMAT)   : date(self::DB_DATE_FORMAT, $object['end']);
+        $sql_data['dtstart'] = $this->_convert_datetime($object['start']);
+        $sql_data['dtend']   = $this->_convert_datetime($object['end']);
 
         // extend date range for recurring events
         if ($object['recurrence'] && $object['_formatobj']) {
             $recurrence = new kolab_date_recurrence($object['_formatobj']);
             $dtend = $recurrence->end() ?: new DateTime('now +10 years');
-            $sql_data['dtend'] = $dtend->format(self::DB_DATE_FORMAT);
+            $sql_data['dtend'] = $this->_convert_datetime($dtend);
         }
 
         // extend start/end dates to spawn all exceptions
         if (is_array($object['exceptions'])) {
             foreach ($object['exceptions'] as $exception) {
                 if (is_a($exception['start'], 'DateTime')) {
-                    $exstart = $exception['start']->format(self::DB_DATE_FORMAT);
+                    $exstart = $this->_convert_datetime($exception['start']);
                     if ($exstart < $sql_data['dtstart']) {
                         $sql_data['dtstart'] = $exstart;
                     }
                 }
                 if (is_a($exception['end'], 'DateTime')) {
-                    $exend = $exception['end']->format(self::DB_DATE_FORMAT);
+                    $exend = $this->_convert_datetime($exception['end']);
                     if ($exend > $sql_data['dtend']) {
                         $sql_data['dtend'] = $exend;
                     }
@@ -64,4 +64,4 @@ class kolab_storage_cache_event extends kolab_storage_cache
 
         return $sql_data;
     }
-}
\ No newline at end of file
+}
diff --git a/plugins/libkolab/lib/kolab_storage_cache_freebusy.php b/plugins/libkolab/lib/kolab_storage_cache_freebusy.php
index d8ab554a..50e48042 100644
--- a/plugins/libkolab/lib/kolab_storage_cache_freebusy.php
+++ b/plugins/libkolab/lib/kolab_storage_cache_freebusy.php
@@ -23,5 +23,20 @@
 
 class kolab_storage_cache_freebusy extends kolab_storage_cache
 {
-        protected $extra_cols = array('dtstart','dtend');
-}
\ No newline at end of file
+    protected $extra_cols = array('dtstart','dtend');
+
+    /**
+     * Helper method to convert the given Kolab object into a dataset to be written to cache
+     *
+     * @override
+     */
+    protected function _serialize($object)
+    {
+        $sql_data = parent::_serialize($object) + array('dtstart' => null, 'dtend' => null);
+
+        $sql_data['dtstart'] = $this->_convert_datetime($object['start']);
+        $sql_data['dtend']   = $this->_convert_datetime($object['end']);
+
+        return $sql_data;
+    }
+}
diff --git a/plugins/libkolab/lib/kolab_storage_cache_journal.php b/plugins/libkolab/lib/kolab_storage_cache_journal.php
index a63577b7..766f1da1 100644
--- a/plugins/libkolab/lib/kolab_storage_cache_journal.php
+++ b/plugins/libkolab/lib/kolab_storage_cache_journal.php
@@ -24,5 +24,19 @@
 class kolab_storage_cache_journal extends kolab_storage_cache
 {
     protected $extra_cols = array('dtstart','dtend');
-    
-}
\ No newline at end of file
+
+    /**
+     * Helper method to convert the given Kolab object into a dataset to be written to cache
+     *
+     * @override
+     */
+    protected function _serialize($object)
+    {
+        $sql_data = parent::_serialize($object) + array('dtstart' => null, 'dtend' => null);
+
+        $sql_data['dtstart'] = $this->_convert_datetime($object['start']);
+        $sql_data['dtend']   = $this->_convert_datetime($object['end']);
+
+        return $sql_data;
+    }
+}
diff --git a/plugins/libkolab/lib/kolab_storage_cache_task.php b/plugins/libkolab/lib/kolab_storage_cache_task.php
index 7bf5c798..8b714e63 100644
--- a/plugins/libkolab/lib/kolab_storage_cache_task.php
+++ b/plugins/libkolab/lib/kolab_storage_cache_task.php
@@ -32,13 +32,11 @@ class kolab_storage_cache_task extends kolab_storage_cache
      */
     protected function _serialize($object)
     {
-        $sql_data = parent::_serialize($object) + array('dtstart' => null, 'dtend' => null);
+        $sql_data = parent::_serialize($object);
 
-        if ($object['start'])
-            $sql_data['dtstart'] = is_object($object['start']) ? $object['start']->format(self::DB_DATE_FORMAT) : date(self::DB_DATE_FORMAT, $object['start']);
-        if ($object['due'])
-            $sql_data['dtend']   = is_object($object['due'])   ? $object['due']->format(self::DB_DATE_FORMAT)   : date(self::DB_DATE_FORMAT, $object['due']);
+        $sql_data['dtstart'] = $this->_convert_datetime($object['start']);
+        $sql_data['dtend']   = $this->_convert_datetime($object['due']);
 
         return $sql_data;
     }
-}
\ No newline at end of file
+}