diff --git a/htdocs/core/lib/functions.lib.php b/htdocs/core/lib/functions.lib.php
index e3a1f8f12dd..b63bb68c4a5 100644
--- a/htdocs/core/lib/functions.lib.php
+++ b/htdocs/core/lib/functions.lib.php
@@ -7631,6 +7631,7 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 				$substitutionarray['__ONLINE_PAYMENT_URL__'] = $paymenturl;
 
 				if (is_object($object) && $object->element == 'propal') {
+					require_once DOL_DOCUMENT_ROOT.'/core/lib/signature.lib.php';
 					$substitutionarray['__ONLINE_SIGN_URL__'] = getOnlineSignatureUrl(0, 'proposal', $object->ref);
 				}
 				if (!empty($conf->global->PROPOSAL_ALLOW_EXTERNAL_DOWNLOAD) && is_object($object) && $object->element == 'propal') {