diff --git a/modules/purchase_trade/lot.py b/modules/purchase_trade/lot.py
index 4318f9a..c90e379 100755
--- a/modules/purchase_trade/lot.py
+++ b/modules/purchase_trade/lot.py
@@ -1393,8 +1393,10 @@ class LotQt(
                     l.sale_line = ll.sale_line
                     Lot.save([l])
                     #ll.lot_gross_quantity -= qt
-                    ll.lot_quantity -= qt
-                    ll.lot_qt -= float(qt)
+                    ll.lot_quantity = (
+                        Decimal(str(ll.lot_quantity or 0)) - qt)
+                    if ll.lot_qt is not None:
+                        ll.lot_qt -= float(qt)
                     Lot.save([ll])
                 else:
                     #Increase forecasted virtual part matched
diff --git a/modules/purchase_trade/tests/test_module.py b/modules/purchase_trade/tests/test_module.py
index 90e6bdf..17a0a83 100644
--- a/modules/purchase_trade/tests/test_module.py
+++ b/modules/purchase_trade/tests/test_module.py
@@ -3488,6 +3488,65 @@ class PurchaseTradeTestCase(ModuleTestCase):
         with self.assertRaises(UserError):
             wizard.transition_matching()
 
+    def test_physical_purchase_matching_keeps_empty_sale_lot_qt(self):
+        'physical purchase matching does not fail when sale lot_qt is empty'
+        physical_lot = Mock(
+            id=101,
+            lot_type='physic',
+            sale_line=None)
+        physical_lot.get_current_quantity_converted.return_value = (
+            Decimal('10'))
+        physical_lot.getVlot_p.return_value = Mock()
+        physical_lot.updateVirtualPart.return_value = True
+        sale_virtual_lot = Mock(
+            sale_line=Mock(),
+            lot_quantity=Decimal('9'),
+            lot_qt=None)
+        sale_virtual_lot.getVlot_s.return_value = sale_virtual_lot
+        sale_lqt = Mock(
+            lot_p=None,
+            lot_s=sale_virtual_lot,
+            lot_quantity=Decimal('9'),
+            lot_unit=None)
+
+        class LotQtMock:
+            def __call__(self, _id):
+                return sale_lqt
+
+            @staticmethod
+            def search(_domain):
+                return []
+
+            @staticmethod
+            def save(_records):
+                return None
+
+        class LotMock:
+            def __call__(self, _id):
+                return physical_lot
+
+            @staticmethod
+            def save(_records):
+                return None
+
+        pool = Mock()
+        pool.get.side_effect = (
+            lambda name: LotQtMock() if name == 'lot.qt' else LotMock())
+        purchase_match = Mock(
+            lot_id=101,
+            lot_r_id=None,
+            lot_matched_qt=Decimal('1'))
+        sale_match = Mock(
+            lot_r_id=2,
+            lot_matched_qt=Decimal('1'))
+
+        with patch.object(lot_module, 'Pool', return_value=pool), \
+                patch.object(lot_module.LotQt, 'search', return_value=[]):
+            lot_module.LotQt.match_lots([purchase_match], [sale_match])
+
+        self.assertIsNone(sale_virtual_lot.lot_qt)
+        self.assertEqual(sale_virtual_lot.lot_quantity, Decimal('8'))
+
     def test_purchase_tolerance_used_is_weighted_line_average(self):
         'purchase tolerance gauge averages line gauges by theoretical quantity'
         unit = Mock()