diff --git a/htdocs/install/mysql/migration/17.0.0-18.0.0.sql b/htdocs/install/mysql/migration/17.0.0-18.0.0.sql
index 0ed686d189f..59c79a5741a 100644
--- a/htdocs/install/mysql/migration/17.0.0-18.0.0.sql
+++ b/htdocs/install/mysql/migration/17.0.0-18.0.0.sql
@@ -413,3 +413,6 @@ ALTER TABLE llx_c_invoice_subtype ADD UNIQUE INDEX uk_c_invoice_subtype (entity,
 
 ALTER TABLE llx_c_propalst ADD COLUMN sortorder smallint DEFAULT 0;
 ALTER TABLE llx_c_stcomm ADD COLUMN sortorder smallint DEFAULT 0;
+
+ALTER TABLE llx_element_time ADD COLUMN ref_ext varchar(32);
+
diff --git a/htdocs/install/mysql/tables/llx_element_time.sql b/htdocs/install/mysql/tables/llx_element_time.sql
index cf346a48ec0..395ca8ff075 100644
--- a/htdocs/install/mysql/tables/llx_element_time.sql
+++ b/htdocs/install/mysql/tables/llx_element_time.sql
@@ -17,6 +17,7 @@
 CREATE TABLE llx_element_time(
 	-- BEGIN MODULEBUILDER FIELDS
 	rowid integer AUTO_INCREMENT PRIMARY KEY NOT NULL,
+    ref_ext varchar(32),                       -- reference into an external system (not used by dolibarr)
     fk_element integer NOT NULL,
     elementtype varchar(32) NOT NULL,
     element_date date,
diff --git a/htdocs/projet/class/api_tasks.class.php b/htdocs/projet/class/api_tasks.class.php
index 8bf6769d8fa..d880ba1ad0d 100644
--- a/htdocs/projet/class/api_tasks.class.php
+++ b/htdocs/projet/class/api_tasks.class.php
@@ -16,10 +16,11 @@
  * along with this program. If not, see <https://www.gnu.org/licenses/>.
  */
 
- use Luracast\Restler\RestException;
+use Luracast\Restler\RestException;
+
+require_once DOL_DOCUMENT_ROOT.'/projet/class/task.class.php';
+require_once DOL_DOCUMENT_ROOT.'/core/lib/date.lib.php';
 
- require_once DOL_DOCUMENT_ROOT.'/projet/class/task.class.php';
- require_once DOL_DOCUMENT_ROOT.'/core/lib/date.lib.php';
 
 /**
  * API class for projects
@@ -29,7 +30,6 @@
  */
 class Tasks extends DolibarrApi
 {
-
 	/**
 	 * @var array   $FIELDS     Mandatory fields, checked when create and update object
 	 */
diff --git a/htdocs/projet/class/task.class.php b/htdocs/projet/class/task.class.php
index 82bbe79edf9..984c24f6ef6 100644
--- a/htdocs/projet/class/task.class.php
+++ b/htdocs/projet/class/task.class.php
@@ -1354,6 +1354,7 @@ class Task extends CommonObjectLine
 		$sql .= " s.nom as thirdparty_name,";
 		$sql .= " s.email as thirdparty_email,";
 		$sql .= " ptt.rowid,";
+		$sql .= " ptt.ref_ext,";
 		$sql .= " ptt.fk_element as fk_task,";
 		$sql .= " ptt.element_date as task_date,";
 		$sql .= " ptt.element_datehour as task_datehour,";
@@ -1404,6 +1405,7 @@ class Task extends CommonObjectLine
 				$newobj->task_label = $obj->task_label;
 
 				$newobj->timespent_line_id = $obj->rowid;
+				$newobj->timespent_line_ref_ext = $obj->ref_ext;
 				$newobj->timespent_line_date = $this->db->jdate($obj->task_date);
 				$newobj->timespent_line_datehour	= $this->db->jdate($obj->task_datehour);
 				$newobj->timespent_line_withhour = $obj->task_date_withhour;