diff --git a/timesheet/inc/class.timesheet_bo.inc.php b/timesheet/inc/class.timesheet_bo.inc.php
index 72b1d9bce8..8c992c35dc 100644
--- a/timesheet/inc/class.timesheet_bo.inc.php
+++ b/timesheet/inc/class.timesheet_bo.inc.php
@@ -560,7 +560,7 @@ class timesheet_bo extends so_sql_cf
 				$sum_extra_cols[$type]{0} = '1';
 				// the $type sum
 				parent::search($criteria,array(
-					$sum_ts_id[$type],"''","''","''",'MIN(ts_start)','SUM(ts_duration) AS ts_duration',
+					(string)$sum_ts_id[$type],"''","''","''",'MIN(ts_start)','SUM(ts_duration) AS ts_duration',
 					($this->quantity_sum ? "SUM(ts_quantity) AS ts_quantity" : '0'),
 					'0','NULL','0','0','0','0','0',"SUM($total_sql) AS ts_total"
 				),'GROUP BY '.$sum_sql[$type],$sum_extra_cols,$wildcard,$empty,$op,'UNION',$filter,$join,$need_full_no_count);