diff --git a/stock_available_immediately/product.py b/stock_available_immediately/product.py
index c41e090b6..845ef63e7 100644
--- a/stock_available_immediately/product.py
+++ b/stock_available_immediately/product.py
@@ -9,8 +9,10 @@ class Product(models.Model):
     """Subtract incoming qty from immediately_usable_qty"""
     _inherit = 'product.product'
 
+    @api.multi
+    @api.depends('virtual_available', 'incoming_qty')
     def _immediately_usable_qty(self):
         """Ignore the incoming goods in the quantity available to promise"""
-        super(Product, self)._immediately_usable_qty()
-        for product in self:
-            product.immediately_usable_qty -= product.incoming_qty
+        super(ProductProduct, self)._immediately_usable_qty()
+        for prod in self:
+            prod.immediately_usable_qty -= prod.incoming_qty