diff --git a/addons/sale/models/sale_order_line.py b/addons/sale/models/sale_order_line.py
index d8c3e0dacc8..69ca835c773 100644
--- a/addons/sale/models/sale_order_line.py
+++ b/addons/sale/models/sale_order_line.py
@@ -941,16 +941,16 @@ class SaleOrderLine(models.Model):
 
     #=== CRUD METHODS ===#
     def _add_precomputed_values(self, vals_list):
-        """ In the specific case where the discount is provided in the create values
+        """ In case an editable precomputed field is provided in the create values
         without being rounded, we have to 'manually' round it otherwise it won't be,
-        because editable precomputed field values are kept 'as is'.
+        because those field values are kept 'as is'.
 
         This is a temporary fix until the problem is fixed in the ORM.
         """
-        precision = self.env['decimal.precision'].precision_get('Discount')
         for vals in vals_list:
-            if vals.get('discount'):
-                vals['discount'] = float_round(vals['discount'], precision_digits=precision)
+            for fname in ('discount', 'product_uom_qty'):
+                if fname in vals:
+                    vals[fname] = self._fields[fname].convert_to_cache(vals[fname], self)
         return super()._add_precomputed_values(vals_list)
 
     @api.model_create_multi
diff --git a/addons/sale/tests/test_sale_prices.py b/addons/sale/tests/test_sale_prices.py
index a5d11f8bb42..5e7b10e8b2b 100644
--- a/addons/sale/tests/test_sale_prices.py
+++ b/addons/sale/tests/test_sale_prices.py
@@ -7,7 +7,7 @@ from datetime import timedelta
 from odoo import fields
 from odoo.fields import Command
 from odoo.tests import Form, tagged
-from odoo.tools import float_compare, mute_logger
+from odoo.tools import float_compare, mute_logger, float_round
 
 from odoo.addons.sale.tests.common import SaleCommon
 
@@ -978,3 +978,21 @@ class TestSalePrices(SaleCommon):
         # 136.36 price tax excluded with discount applied
         self.assertEqual(order.amount_undiscounted, 272.72)
         self.assertEqual(line.price_subtotal, 136.36)
+
+    def test_product_quantity_rounding(self):
+        """When adding a sale order line, product quantity should be rounded
+        according to decimal precision"""
+        order = self.empty_order
+
+        product_uom_qty = 0.333333
+        order.order_line = [Command.create({
+            'product_id': self.product.id,
+            'product_uom_qty': product_uom_qty,
+            'price_unit': 75.0,
+        })]
+        order.action_confirm()
+        line = order.order_line
+        quantity_precision = self.env['decimal.precision'].precision_get('Product Unit of Measure')
+        expected_price_subtotal = line.price_unit * float_round(product_uom_qty, precision_digits=quantity_precision)
+        self.assertAlmostEqual(line.price_subtotal, expected_price_subtotal)
+        self.assertEqual(order.amount_total, order.tax_totals.get('amount_total'))