diff --git a/htdocs/user/card.php b/htdocs/user/card.php
index d71922cbfd5..2325ab7ab53 100644
--- a/htdocs/user/card.php
+++ b/htdocs/user/card.php
@@ -538,7 +538,7 @@ if (empty($reshook)) {
 						if (!empty($contact->socid)) {
 							$sql .= ", fk_soc=".((int) $contact->socid);
 						} elseif ($socid > 0) {
-							$sql .= ", fk_soc=''";
+							$sql .= ", fk_soc = null";
 							setEventMessages($langs->trans("WarningUserDifferentContactSocid"), '', 'warnings'); // Add message if post socid != $contact->socid
 						}
 						$sql .= " WHERE rowid = ".((int) $object->id);