diff --git a/htdocs/bom/class/bom.class.php b/htdocs/bom/class/bom.class.php
index 78b7e78f91f..b61a65f95a2 100644
--- a/htdocs/bom/class/bom.class.php
+++ b/htdocs/bom/class/bom.class.php
@@ -667,10 +667,10 @@ class BOM extends CommonObject
 	 * @param	float	$efficiency				Efficiency in MO
 	 * @param	int		$position				Position of BOM-Line in BOM-Lines
 	 * @param	string	$import_key				Import Key
-	 * @param	int	$fk_unit					Unit of line
+	 * @param	int		$fk_unit					Unit of line
 	 * @return	int								<0 if KO, Id of updated BOM-Line if OK
 	 */
-	public function updateLine($rowid, $qty, $qty_frozen = 0, $disable_stock_change = 0, $efficiency = 1.0, $position = -1, $import_key = null, $fk_unit)
+	public function updateLine($rowid, $qty, $qty_frozen = 0, $disable_stock_change = 0, $efficiency = 1.0, $position = -1, $import_key = null, $fk_unit = 0)
 	{
 		global $mysoc, $conf, $langs, $user;
 
@@ -740,7 +740,7 @@ class BOM extends CommonObject
 			$this->line->efficiency = $efficiency;
 			$this->line->import_key = $import_key;
 			$this->line->position = $rankToUse;
-			$this->line->fk_unit = $fk_unit;
+			if(!empty($fk_unit)) $this->line->fk_unit = $fk_unit;
 
 			$result = $this->line->update($user);