diff --git a/htdocs/mrp/class/api_mos.class.php b/htdocs/mrp/class/api_mos.class.php
index 4b185f4b304..1c8435d65cf 100644
--- a/htdocs/mrp/class/api_mos.class.php
+++ b/htdocs/mrp/class/api_mos.class.php
@@ -736,7 +736,7 @@ class Mos extends DolibarrApi
 	 *
 	 * @return void
 	 */
-	private function checkRefNumbering(): void
+	private function checkRefNumbering()
 	{
 		$ref = substr($this->mo->ref, 1, 4);
 		if ($this->mo->status > 0 && $ref == 'PROV') {