diff --git a/htdocs/compta/facture.php b/htdocs/compta/facture.php
index abce93d9d90591f9be6c68d1c348f9744770264d..f900e2889a3a60f5d8152d0c16b88df36bfae798 100644
--- a/htdocs/compta/facture.php
+++ b/htdocs/compta/facture.php
@@ -812,14 +812,14 @@ if (empty($reshook))
 	                        $line->fk_parent_line = $fk_parent_line;
 
 	                        $line->subprice =-$line->subprice; // invert price for object
-	                        $line->pa_ht = -$line->pa_ht;
+	                        $line->pa_ht = $line->pa_ht;       // we choosed to have buy/cost price always positive, so no revert of sign here
 	                        $line->total_ht=-$line->total_ht;
 	                        $line->total_tva=-$line->total_tva;
 	                        $line->total_ttc=-$line->total_ttc;
 	                        $line->total_localtax1=-$line->total_localtax1;
 	                        $line->total_localtax2=-$line->total_localtax2;
 
-	                        $result = $line->insert();
+	                        $result = $line->insert(0, 1);     // When creating credit note with same lines than source, we must ignore error if discount alreayd linked
 
 	                        $object->lines[] = $line; // insert new line in current object
 
diff --git a/htdocs/compta/facture/class/facture.class.php b/htdocs/compta/facture/class/facture.class.php
index 2d76242ccc41f119e511a6bbfc27d9a89c7236fd..36046fa80101dc579f23f93ccb2a11a511ccc0ae 100644
--- a/htdocs/compta/facture/class/facture.class.php
+++ b/htdocs/compta/facture/class/facture.class.php
@@ -4096,10 +4096,11 @@ class FactureLigne extends CommonInvoiceLine
 	/**
 	 *	Insert line into database
 	 *
-	 *	@param      int		$notrigger		1 no triggers
-	 *	@return		int						<0 if KO, >0 if OK
+	 *	@param      int		$notrigger		                 1 no triggers
+	 *  @param      int     $noerrorifdiscountalreadylinked  1=Do not make error if lines is linked to a discount and discount already linked to another
+	 *	@return		int						                 <0 if KO, >0 if OK
 	 */
-	function insert($notrigger=0)
+	function insert($notrigger=0, $noerrorifdiscountalreadylinked=0)
 	{
 		global $langs,$user,$conf;
 
@@ -4243,13 +4244,16 @@ class FactureLigne extends CommonInvoiceLine
 					// Check if discount was found
 					if ($result > 0)
 					{
-						// Check if discount not already affected to another invoice
-						if ($discount->fk_facture)
+					    // Check if discount not already affected to another invoice
+						if ($discount->fk_facture_line > 0)
 						{
-							$this->error=$langs->trans("ErrorDiscountAlreadyUsed",$discount->id);
-							dol_syslog(get_class($this)."::insert Error ".$this->error, LOG_ERR);
-							$this->db->rollback();
-							return -3;
+						    if (empty($noerrorifdiscountalreadylinked))
+						    {
+    							$this->error=$langs->trans("ErrorDiscountAlreadyUsed",$discount->id);
+    							dol_syslog(get_class($this)."::insert Error ".$this->error, LOG_ERR);
+    							$this->db->rollback();
+    							return -3;
+						    }
 						}
 						else
 						{