diff --git a/htdocs/comm/propal/class/propal.class.php b/htdocs/comm/propal/class/propal.class.php
index 0e6ea992249..dadc49c7b75 100644
--- a/htdocs/comm/propal/class/propal.class.php
+++ b/htdocs/comm/propal/class/propal.class.php
@@ -2426,7 +2426,7 @@ class PropaleLigne
 		$sql.= ' info_bits, ';
 		$sql.= ' total_ht, total_tva, total_localtax1, total_localtax2, total_ttc, special_code, rang, marge_tx, marque_tx)';
 		$sql.= " VALUES (".$this->fk_propal.",";
-		$sql.= " ".$this->fk_parent_line.",";
+		$sql.= " ".($this->fk_parent_line>0?"'".$this->fk_parent_line."'":"null").",";
 		$sql.= " '".$this->db->escape($this->desc)."',";
 		$sql.= " ".($this->fk_product?"'".$this->fk_product."'":"null").",";
 		$sql.= " '".$this->product_type."',";
diff --git a/htdocs/commande/class/commande.class.php b/htdocs/commande/class/commande.class.php
index 24fee33b743..47444383269 100644
--- a/htdocs/commande/class/commande.class.php
+++ b/htdocs/commande/class/commande.class.php
@@ -2727,7 +2727,7 @@ class OrderLine
 		$sql.= ' special_code, rang, marge_tx, marque_tx,';
 		$sql.= ' info_bits, total_ht, total_tva, total_localtax1, total_localtax2, total_ttc, date_start, date_end)';
 		$sql.= " VALUES (".$this->fk_commande.",";
-		$sql.= " ".$this->fk_parent_line.",";
+		$sql.= " ".($this->fk_parent_line>0?"'".$this->fk_parent_line."'":"null").",";
 		$sql.= " '".$this->db->escape($this->desc)."',";
 		$sql.= " '".price2num($this->qty)."',";
 		$sql.= " '".price2num($this->tva_tx)."',";
diff --git a/htdocs/compta/facture/class/facture.class.php b/htdocs/compta/facture/class/facture.class.php
index d807642495d..da5b3f2fcb9 100644
--- a/htdocs/compta/facture/class/facture.class.php
+++ b/htdocs/compta/facture/class/facture.class.php
@@ -3256,7 +3256,7 @@ class FactureLigne
         $sql.= ' rang, special_code,';
         $sql.= ' info_bits, total_ht, total_tva, total_localtax1, total_localtax2, total_ttc)';
         $sql.= " VALUES (".$this->fk_facture.",";
-        $sql.= " ".$this->fk_parent_line.",";
+        $sql.= " ".($this->fk_parent_line>0?"'".$this->fk_parent_line."'":"null").",";
         $sql.= " '".$this->db->escape($this->desc)."',";
         $sql.= " ".price2num($this->qty).",";
         $sql.= " ".price2num($this->tva_tx).",";