diff --git a/htdocs/comm/propal/class/propal.class.php b/htdocs/comm/propal/class/propal.class.php
index f36f261cc19..22dac7fa2a9 100644
--- a/htdocs/comm/propal/class/propal.class.php
+++ b/htdocs/comm/propal/class/propal.class.php
@@ -783,7 +783,7 @@ class Propal extends CommonObject
 
 			// Rang to use
 			$ranktouse = $rang;
-			if ($ranktouse == -1) {
+			if (empty($ranktouse) || $ranktouse == -1) {
 				$rangmax = $this->line_max($fk_parent_line);
 				$ranktouse = $rangmax + 1;
 			}
diff --git a/htdocs/commande/class/commande.class.php b/htdocs/commande/class/commande.class.php
index 960ea46ed30..1640c361d0b 100644
--- a/htdocs/commande/class/commande.class.php
+++ b/htdocs/commande/class/commande.class.php
@@ -1763,7 +1763,7 @@ class Commande extends CommonOrder
 			// Rang to use
 			$ranktouse = $rang;
 
-			if ($ranktouse == -1) {
+			if (empty($ranktouse) || $ranktouse == -1) {
 				$rangmax = $this->line_max($fk_parent_line);
 				$ranktouse = $rangmax + 1;
 			}
diff --git a/htdocs/compta/facture/class/facture.class.php b/htdocs/compta/facture/class/facture.class.php
index 54ec34e1fd0..7898437bb39 100644
--- a/htdocs/compta/facture/class/facture.class.php
+++ b/htdocs/compta/facture/class/facture.class.php
@@ -4397,7 +4397,7 @@ class Facture extends CommonInvoice
 
 			// Rank to use
 			$ranktouse = $rang;
-			if ($ranktouse == -1) {
+			if (empty($ranktouse) || $ranktouse == -1) {
 				$rangmax = $this->line_max($fk_parent_line);
 				$ranktouse = $rangmax + 1;
 			}