diff --git a/apps/calendar/ajax/editevent.php b/apps/calendar/ajax/editevent.php
index a60b0946ad..46feb06849 100644
--- a/apps/calendar/ajax/editevent.php
+++ b/apps/calendar/ajax/editevent.php
@@ -35,6 +35,13 @@ if($errarr){
 		exit;
 	}
 	$vcalendar = OC_Calendar_Object::parse($data['calendardata']);
+
+	$last_modified = $vcalendar->VEVENT->__get('LAST-MODIFIED');
+	if($last_modified && $_POST['lastmodified'] != $last_modified->getDateTime()->format('U')){
+		OC_JSON::error(array('modified'=>true));
+		exit;
+	}
+
 	OC_Calendar_Object::updateVCalendarFromRequest($_POST, $vcalendar);
 	$result = OC_Calendar_Object::edit($id, $vcalendar->serialize());
 	if ($data['calendarid'] != $cal) {
diff --git a/apps/calendar/ajax/editeventform.php b/apps/calendar/ajax/editeventform.php
index e6dc813660..63c7293407 100644
--- a/apps/calendar/ajax/editeventform.php
+++ b/apps/calendar/ajax/editeventform.php
@@ -63,9 +63,16 @@ foreach($categories as $category){
 }
 $repeat = isset($vevent->CATEGORY) ? $vevent->CATEGORY->value : '';
 $description = isset($vevent->DESCRIPTION) ? $vevent->DESCRIPTION->value : '';
+$last_modified = $vevent->__get('LAST-MODIFIED');
+if ($last_modified){
+	$lastmodified = $last_modified->getDateTime()->format('U');
+}else{
+	$lastmodified = 0;
+}
 
 $tmpl = new OC_Template('calendar', 'part.editevent');
 $tmpl->assign('id', $id);
+$tmpl->assign('lastmodified', $lastmodified);
 $tmpl->assign('calendar_options', $calendar_options);
 $tmpl->assign('category_options', $category_options);
 $tmpl->assign('repeat_options', $repeat_options);
diff --git a/apps/calendar/ajax/events.php b/apps/calendar/ajax/events.php
index 5ee2ffb627..66aeb1a35b 100644
--- a/apps/calendar/ajax/events.php
+++ b/apps/calendar/ajax/events.php
@@ -40,9 +40,16 @@ foreach($events as $event)
 		$return_event['end'] = $end_dt->format('Y-m-d H:i:s');
 		$return_event['allDay'] = false;
 	}
-	$return_event['id'] = $event['id'];
+	$return_event['id'] = (int)$event['id'];
 	$return_event['title'] = $event['summary'];
 	$return_event['description'] = isset($vevent->DESCRIPTION)?$vevent->DESCRIPTION->value:'';
+	$last_modified = $vevent->__get('LAST-MODIFIED');
+	if ($last_modified){
+		$lastmodified = $last_modified->getDateTime()->format('U');
+	}else{
+		$lastmodified = 0;
+	}
+	$return_event['lastmodified'] = (int)$lastmodified;
 	$return[] = $return_event;
 }
 OC_JSON::encodedPrint($return);
diff --git a/apps/calendar/ajax/moveevent.php b/apps/calendar/ajax/moveevent.php
index 834a454fca..6b315a3921 100644
--- a/apps/calendar/ajax/moveevent.php
+++ b/apps/calendar/ajax/moveevent.php
@@ -25,6 +25,12 @@ $delta->i = $_POST['minuteDelta'];
 $vcalendar = OC_Calendar_Object::parse($data['calendardata']);
 $vevent = $vcalendar->VEVENT;
 
+$last_modified = $vevent->__get('LAST-MODIFIED');
+if($last_modified && $_POST['lastmodified'] != $last_modified->getDateTime()->format('U')){
+	OC_JSON::error();
+	exit;
+}
+
 $dtstart = $vevent->DTSTART;
 $dtend = OC_Calendar_Object::getDTEndFromVEvent($vevent);
 $start_type = $dtstart->getDateType();
@@ -50,4 +56,4 @@ $dtstamp->setDateTime($now, Sabre_VObject_Element_DateTime::UTC);
 $vevent->DTSTAMP = $dtstamp;
 
 $result = OC_Calendar_Object::edit($id, $vcalendar->serialize());
-OC_JSON::success();
+OC_JSON::success(array('lastmodified'=>(int)$now->format('U')));
diff --git a/apps/calendar/ajax/resizeevent.php b/apps/calendar/ajax/resizeevent.php
index 639ef91ee7..28a185411e 100644
--- a/apps/calendar/ajax/resizeevent.php
+++ b/apps/calendar/ajax/resizeevent.php
@@ -25,6 +25,12 @@ $delta->i = $_POST['minuteDelta'];
 $vcalendar = OC_Calendar_Object::parse($data['calendardata']);
 $vevent = $vcalendar->VEVENT;
 
+$last_modified = $vevent->__get('LAST-MODIFIED');
+if($last_modified && $_POST['lastmodified'] != $last_modified->getDateTime()->format('U')){
+	OC_JSON::error();
+	exit;
+}
+
 $dtend = OC_Calendar_Object::getDTEndFromVEvent($vevent);
 $end_type = $dtend->getDateType();
 $dtend->setDateTime($dtend->getDateTime()->add($delta), $end_type);
@@ -40,4 +46,4 @@ $dtstamp->setDateTime($now, Sabre_VObject_Element_DateTime::UTC);
 $vevent->DTSTAMP = $dtstamp;
 
 $result = OC_Calendar_Object::edit($id, $vcalendar->serialize());
-OC_JSON::success();
+OC_JSON::success(array('lastmodified'=>$now->format('U')));
diff --git a/apps/calendar/js/calendar.js b/apps/calendar/js/calendar.js
index e943bee705..af5ecd8281 100644
--- a/apps/calendar/js/calendar.js
+++ b/apps/calendar/js/calendar.js
@@ -108,23 +108,27 @@ Calendar={
 		},
 		moveEvent:function(event, dayDelta, minuteDelta, allDay, revertFunc){
 			$('.tipsy').remove();
-			$.post(OC.filePath('calendar', 'ajax', 'moveevent.php'), { id: event.id, dayDelta: dayDelta, minuteDelta: minuteDelta, allDay: allDay?1:0},
+			$.post(OC.filePath('calendar', 'ajax', 'moveevent.php'), { id: event.id, dayDelta: dayDelta, minuteDelta: minuteDelta, allDay: allDay?1:0, lastmodified: event.lastmodified},
 			function(data) {
 				if (data.status == 'success'){
+					event.lastmodified = data.lastmodified;
 					console.log("Event moved successfully");
 				}else{
 					revertFunc();
+					$('#calendar_holder').fullCalendar('refetchEvents');
 				}
 			});
 		},
 		resizeEvent:function(event, dayDelta, minuteDelta, revertFunc){
 			$('.tipsy').remove();
-			$.post(OC.filePath('calendar', 'ajax', 'resizeevent.php'), { id: event.id, dayDelta: dayDelta, minuteDelta: minuteDelta},
+			$.post(OC.filePath('calendar', 'ajax', 'resizeevent.php'), { id: event.id, dayDelta: dayDelta, minuteDelta: minuteDelta, lastmodified: event.lastmodified},
 			function(data) {
 				if (data.status == 'success'){
+					event.lastmodified = data.lastmodified;
 					console.log("Event resized successfully");
 				}else{
 					revertFunc();
+					$('#calendar_holder').fullCalendar('refetchEvents');
 				}
 			});
 		},
diff --git a/apps/calendar/lib/object.php b/apps/calendar/lib/object.php
index 9a343a2376..221df2b3af 100644
--- a/apps/calendar/lib/object.php
+++ b/apps/calendar/lib/object.php
@@ -307,6 +307,7 @@ class OC_Calendar_Object{
 	 */
 	public static function parse($data){
 		try {
+			Sabre_VObject_Reader::$elementMap['LAST-MODIFIED'] = 'Sabre_VObject_Element_DateTime';
 			$calendar = Sabre_VObject_Reader::read($data);
 			return $calendar;
 		} catch (Exception $e) {
diff --git a/apps/calendar/templates/part.editevent.php b/apps/calendar/templates/part.editevent.php
index ae969f2dc3..b3acfc4a07 100644
--- a/apps/calendar/templates/part.editevent.php
+++ b/apps/calendar/templates/part.editevent.php
@@ -1,6 +1,7 @@
 <div id="event" title="<?php echo $l->t("Edit an event");?>">
 	<form id="event_form">
 		<input type="hidden" name="id" value="<?php echo $_['id'] ?>">
+		<input type="hidden" name="lastmodified" value="<?php echo $_['lastmodified'] ?>">
 <?php echo $this->inc("part.eventform"); ?>
 	<div style="width: 100%;text-align: center;color: #FF1D1D;" id="errorbox"></div>
 	<span id="actions">