diff --git a/calendar/setup/setup.inc.php b/calendar/setup/setup.inc.php
index 67642d210a..be7330243e 100755
--- a/calendar/setup/setup.inc.php
+++ b/calendar/setup/setup.inc.php
@@ -10,7 +10,7 @@
  */
 
 $setup_info['calendar']['name']    = 'calendar';
-$setup_info['calendar']['version'] = '1.9.003';
+$setup_info['calendar']['version'] = '1.9.004';
 $setup_info['calendar']['app_order'] = 3;
 $setup_info['calendar']['enable']  = 1;
 $setup_info['calendar']['index']   = 'calendar.calendar_uiviews.index';
@@ -68,3 +68,5 @@ $setup_info['calendar']['check_install'] = array(
 		'from' => 'Calendar',
 	),
 );
+
+
diff --git a/calendar/setup/tables_current.inc.php b/calendar/setup/tables_current.inc.php
index 8bf472d78d..aa17d845ee 100644
--- a/calendar/setup/tables_current.inc.php
+++ b/calendar/setup/tables_current.inc.php
@@ -36,7 +36,7 @@ $phpgw_baseline = array(
 		),
 		'pk' => array('cal_id'),
 		'fk' => array(),
-		'ix' => array('cal_uid','cal_owner','cal_deleted','caldav_name'),
+		'ix' => array('cal_uid','cal_owner','cal_modified','cal_deleted','caldav_name'),
 		'uc' => array()
 	),
 	'egw_cal_holidays' => array(
@@ -82,7 +82,7 @@ $phpgw_baseline = array(
 		),
 		'pk' => array('cal_id','cal_recur_date','cal_user_type','cal_user_id'),
 		'fk' => array(),
-		'ix' => array(array('cal_user_type','cal_user_id')),
+		'ix' => array('cal_user_modified',array('cal_user_type','cal_user_id')),
 		'uc' => array()
 	),
 	'egw_cal_extra' => array(
diff --git a/calendar/setup/tables_update.inc.php b/calendar/setup/tables_update.inc.php
index 12944c77e6..7ffb888c75 100644
--- a/calendar/setup/tables_update.inc.php
+++ b/calendar/setup/tables_update.inc.php
@@ -2067,3 +2067,14 @@ function calendar_upgrade1_9_002()
 	return $GLOBALS['setup_info']['calendar']['currentver'] = '1.9.003';
 }
 
+
+/**
+ * Add index for cal_modified and cal_user_modified to improve ctag and etag generation on big installtions
+ */
+function calendar_upgrade1_9_003()
+{
+	$GLOBALS['egw_setup']->oProc->CreateIndex('egw_cal','cal_modified');
+	$GLOBALS['egw_setup']->oProc->CreateIndex('egw_cal_user','cal_user_modified');
+
+	return $GLOBALS['setup_info']['calendar']['currentver'] = '1.9.004';
+}