diff --git a/htdocs/eventorganization/conferenceorbooth_list.php b/htdocs/eventorganization/conferenceorbooth_list.php
index d72941d2885..0b585a03ca2 100644
--- a/htdocs/eventorganization/conferenceorbooth_list.php
+++ b/htdocs/eventorganization/conferenceorbooth_list.php
@@ -282,7 +282,7 @@ if ($projectid > 0) {
 	// Title
 	$morehtmlref .= $project->title;
 	// Thirdparty
-	if ($project->thirdparty->id > 0) {
+	if (isset($project->thirdparty->id) && $project->thirdparty->id > 0) {
 		$morehtmlref .= '<br>'.$langs->trans('ThirdParty').' : '.$project->thirdparty->getNomUrl(1, 'project');
 	}
 	$morehtmlref .= '</div>';