diff --git a/htdocs/core/modules/project/task/doc/doc_generic_task_odt.modules.php b/htdocs/core/modules/project/task/doc/doc_generic_task_odt.modules.php
index aeb0576cc6fdf..a20c933500a73 100644
--- a/htdocs/core/modules/project/task/doc/doc_generic_task_odt.modules.php
+++ b/htdocs/core/modules/project/task/doc/doc_generic_task_odt.modules.php
@@ -208,8 +208,8 @@ public function get_substitutionarray_tasks($task, $outputlangs, $array_key = 't
 			'task_public' => $task->public,
 			'task_date_start' => dol_print_date($task->date_start, 'day'),
 			'task_date_end' => dol_print_date($task->date_end, 'day'),
-			'task_note_private' => $task->note_private,
-			'task_note_public' => $task->note_public
+			'task_note_private' => (string) $task->note_private,
+			'task_note_public' => (string) $task->note_public
 		);
 
 		// Retrieve extrafields