diff --git a/addons/sale_stock/models/sale_order.py b/addons/sale_stock/models/sale_order.py
index 42183c76c44..445533135b6 100644
--- a/addons/sale_stock/models/sale_order.py
+++ b/addons/sale_stock/models/sale_order.py
@@ -80,25 +80,17 @@ class SaleOrder(models.Model):
         if values.get('order_line') and self.state == 'sale':
             for order in self:
                 to_log = {}
-                order_lines_to_run = self.env['sale.order.line']
                 for order_line in order.order_line:
-                    if order_line not in pre_order_line_qty:
-                        order_lines_to_run |= order_line
-                    elif float_compare(order_line.product_uom_qty, pre_order_line_qty[order_line], order_line.product_uom.rounding) < 0:
-                        to_log[order_line] = (order_line.product_uom_qty, pre_order_line_qty[order_line])
-                    elif float_compare(order_line.product_uom_qty, pre_order_line_qty[order_line], order_line.product_uom.rounding) > 0:
-                        order_lines_to_run |= order_line
+                    if float_compare(order_line.product_uom_qty, pre_order_line_qty.get(order_line, 0.0), order_line.product_uom.rounding) < 0:
+                        to_log[order_line] = (order_line.product_uom_qty, pre_order_line_qty.get(order_line, 0.0))
                 if to_log:
                     documents = self.env['stock.picking']._log_activity_get_documents(to_log, 'move_ids', 'UP')
                     order._log_decrease_ordered_quantity(documents)
-                if order_lines_to_run:
-                    order_lines_to_run._action_launch_stock_rule(pre_order_line_qty)
         return res
 
     def _action_confirm(self):
-        for order in self:
-            order.order_line._action_launch_stock_rule()
-        super(SaleOrder, self)._action_confirm()
+        self.order_line._action_launch_stock_rule()
+        return super(SaleOrder, self)._action_confirm()
 
     @api.depends('picking_ids')
     def _compute_picking_ids(self):
@@ -337,6 +329,18 @@ class SaleOrderLine(models.Model):
         lines.filtered(lambda line: line.state == 'sale')._action_launch_stock_rule()
         return lines
 
+    def write(self, values):
+        lines = self.env['sale.order.line']
+        if 'product_uom_qty' in values:
+            precision = self.env['decimal.precision'].precision_get('Product Unit of Measure')
+            lines = self.filtered(
+                lambda r: r.state == 'sale' and not r.is_expense and float_compare(r.product_uom_qty, values['product_uom_qty'], precision_digits=precision) == -1)
+        previous_product_uom_qty = {line.id: line.product_uom_qty for line in lines}
+        res = super(SaleOrderLine, self).write(values)
+        if lines:
+            lines._action_launch_stock_rule(previous_product_uom_qty)
+        return res
+
     @api.depends('order_id.state')
     def _compute_invoice_status(self):
         super(SaleOrderLine, self)._compute_invoice_status()
diff --git a/addons/sale_stock/tests/test_sale_stock.py b/addons/sale_stock/tests/test_sale_stock.py
index 580e207fcfa..073f1568c1a 100644
--- a/addons/sale_stock/tests/test_sale_stock.py
+++ b/addons/sale_stock/tests/test_sale_stock.py
@@ -328,6 +328,14 @@ class TestSaleStock(TestSale):
             elif backorder_move.product_id.id == item2.id:
                 self.assertEqual(backorder_move.product_qty, 2)
 
+        # add a new sale order lines
+        self.so.write({
+            'order_line': [
+                (0, 0, {'name': item1.name, 'product_id': item1.id, 'product_uom_qty': 1, 'product_uom': item1.uom_id.id, 'price_unit': item1.list_price}),
+            ]
+        })
+        self.assertEqual(sum(backorder.move_lines.filtered(lambda m: m.product_id.id == item1.id).mapped('product_qty')), 2)
+
     def test_05_create_picking_update_saleorderline(self):
         """ Same test than test_04 but only with enough products in stock so that the reservation
         is successful.