diff --git a/plugins/libcalendaring/libvcalendar.php b/plugins/libcalendaring/libvcalendar.php
index b4fdce32..f64499fb 100644
--- a/plugins/libcalendaring/libvcalendar.php
+++ b/plugins/libcalendaring/libvcalendar.php
@@ -576,9 +576,10 @@ class libvcalendar
      */
     public static function datetime_prop($name, $dt, $utc = false, $dateonly = null)
     {
+        $is_utc = $utc || (($tz = $dt->getTimezone()) && in_array($tz->getName(), array('UTC','GMT','Z')));
         $vdt = new VObject\Property\DateTime($name);
         $vdt->setDateTime($dt, $dt->_dateonly || $dateonly ? VObject\Property\DateTime::DATE :
-            ($utc ? VObject\Property\DateTime::UTC : VObject\Property\DateTime::LOCALTZ));
+            ($is_utc ? VObject\Property\DateTime::UTC : VObject\Property\DateTime::LOCALTZ));
         return $vdt;
     }
 
diff --git a/plugins/libcalendaring/tests/libvcalendar.php b/plugins/libcalendaring/tests/libvcalendar.php
index c8911454..34044736 100644
--- a/plugins/libcalendaring/tests/libvcalendar.php
+++ b/plugins/libcalendaring/tests/libvcalendar.php
@@ -323,6 +323,19 @@ class libvcalendar_test extends PHPUnit_Framework_TestCase
         $this->assertEquals($num, substr_count($output, 'END:VEVENT'),   "VEVENT encapsulation END");
     }
 
+    function test_datetime()
+    {
+        $localtime = libvcalendar::datetime_prop('DTSTART', new DateTime('2013-09-01 12:00:00', new DateTimeZone('Europe/Berlin')));
+        $localdate = libvcalendar::datetime_prop('DTSTART', new DateTime('2013-09-01', new DateTimeZone('Europe/Berlin')), false, true);
+        $utctime   = libvcalendar::datetime_prop('DTSTART', new DateTime('2013-09-01 12:00:00', new DateTimeZone('UTC')));
+        $asutctime = libvcalendar::datetime_prop('DTSTART', new DateTime('2013-09-01 12:00:00', new DateTimeZone('Europe/Berlin')), true);
+
+        $this->assertContains('TZID=Europe/Berlin', $localtime->serialize());
+        $this->assertContains('VALUE=DATE', $localdate->serialize());
+        $this->assertContains('20130901T120000Z', $utctime->serialize());
+        $this->assertContains('20130901T100000Z', $asutctime->serialize());
+    }
+
     function get_attachment_data($id, $event)
     {
         return $this->attachment_data;