diff --git a/htdocs/contact/class/contact.class.php b/htdocs/contact/class/contact.class.php
index 95897271f1a..b5f714131d9 100644
--- a/htdocs/contact/class/contact.class.php
+++ b/htdocs/contact/class/contact.class.php
@@ -311,7 +311,7 @@ class Contact extends CommonObject
 		$sql .= ", email='".$this->db->escape($this->email)."'";
 		$sql .= ", skype='".$this->db->escape($this->skype)."'";
 		$sql .= ", photo='".$this->db->escape($this->photo)."'";
-		$sql .= ", birthday=".($this->birthday ? "'".$this->db->idate($this->birthday)."'" : "");
+		$sql .= ", birthday=".($this->birthday ? "'".$this->db->idate($this->birthday)."'" : "null");
 		$sql .= ", note_private = ".(isset($this->note_private)?"'".$this->db->escape($this->note_private)."'":"null");
 		$sql .= ", note_public = ".(isset($this->note_public)?"'".$this->db->escape($this->note_public)."'":"null");
 		$sql .= ", phone = ".(isset($this->phone_pro)?"'".$this->db->escape($this->phone_pro)."'":"null");