diff --git a/htdocs/projet/card.php b/htdocs/projet/card.php
index 6925294ec2d..3c7e60e8173 100644
--- a/htdocs/projet/card.php
+++ b/htdocs/projet/card.php
@@ -271,7 +271,7 @@ if (empty($reshook)) {
 				$db->commit();
 
 				if (!empty($backtopage)) {
-					$backtopage = preg_replace('/--IDFORBACKTOPAGE--|__ID__/', $object->id, $backtopage); // New method to autoselect project after a New on another form object creation
+					$backtopage = preg_replace('/--IDFORBACKTOPAGE--|__ID__/', (string) $object->id, $backtopage); // New method to autoselect project after a New on another form object creation
 					$backtopage = $backtopage.'&projectid='.$object->id; // Old method
 					header("Location: ".$backtopage);
 					exit;
@@ -508,7 +508,7 @@ if (empty($reshook)) {
 
 			if (!empty($_SESSION['pageforbacktolist']) && !empty($_SESSION['pageforbacktolist']['project'])) {
 				$tmpurl = $_SESSION['pageforbacktolist']['project'];
-				$tmpurl = preg_replace('/__SOCID__/', $object->socid, $tmpurl);
+				$tmpurl = preg_replace('/__SOCID__/', (string) $object->socid, $tmpurl);
 				$urlback = $tmpurl.(preg_match('/\?/', $tmpurl) ? '&' : '?'). 'restore_lastsearch_values=1';
 			} else {
 				$urlback = DOL_URL_ROOT.'/projet/list.php?restore_lastsearch_values=1';
@@ -1300,7 +1300,7 @@ if ($action == 'create' && $user->hasRight('projet', 'creer')) {
 
 		if (!empty($_SESSION['pageforbacktolist']) && !empty($_SESSION['pageforbacktolist']['project'])) {
 			$tmpurl = $_SESSION['pageforbacktolist']['project'];
-			$tmpurl = preg_replace('/__SOCID__/', $object->socid, $tmpurl);
+			$tmpurl = preg_replace('/__SOCID__/', (string) $object->socid, $tmpurl);
 			$linkback = '<a href="'.$tmpurl.(preg_match('/\?/', $tmpurl) ? '&' : '?'). 'restore_lastsearch_values=1">'.$langs->trans("BackToList").'</a>';
 		} else {
 			$linkback = '<a href="'.DOL_URL_ROOT.'/projet/list.php?restore_lastsearch_values=1">'.$langs->trans("BackToList").'</a>';