diff --git a/classes/stock/StockManagerInterface.php b/classes/stock/StockManagerInterface.php
index 1ff4eb669..b4104faaa 100644
--- a/classes/stock/StockManagerInterface.php
+++ b/classes/stock/StockManagerInterface.php
@@ -52,7 +52,7 @@ interface StockManagerInterface
 	 * @param int $id_supplier_order optionnal
 	 * @return bool
 	 */
-	public function addProduct($id_product, $id_product_attribute, Warehouse $warehouse, $quantity, $id_stock_movement_reason, $price_te, $is_usable, $id_supplier_order = null);
+	public function addProduct($id_product, $id_product_attribute, Warehouse $warehouse, $quantity, $id_stock_movement_reason, $price_te, $is_usable = true, $id_supplier_order = null);
 
 	/**
 	 * For a given product, removes a given quantity
@@ -66,7 +66,7 @@ interface StockManagerInterface
 	 * @param int $id_order Optionnal
 	 * @return array - empty if an error occured | details of removed products quantities with corresponding prices otherwise
 	 */
-	public function removeProduct($id_product, $id_product_attribute, Warehouse $warehouse, $quantity, $id_stock_movement_reason, $is_usable, $id_order = null);
+	public function removeProduct($id_product, $id_product_attribute, Warehouse $warehouse, $quantity, $id_stock_movement_reason, $is_usable = true, $id_order = null);
 
 	/**
 	 * For a given product, returns its physical quantity