diff --git a/timesheet/inc/class.timesheet_merge.inc.php b/timesheet/inc/class.timesheet_merge.inc.php
index 08ac4c3361..26749d2564 100644
--- a/timesheet/inc/class.timesheet_merge.inc.php
+++ b/timesheet/inc/class.timesheet_merge.inc.php
@@ -49,6 +49,10 @@ class timesheet_merge extends bo_merge
 	{
 		parent::__construct();
 		$this->bo = new timesheet_bo();
+		$this->date_fields += array(
+			'ts_start',
+			'ts_modified',
+		);
 	}
 
 	/**