diff --git a/modules/purchase_trade/lot.py b/modules/purchase_trade/lot.py
index a6712b1..7159ba5 100755
--- a/modules/purchase_trade/lot.py
+++ b/modules/purchase_trade/lot.py
@@ -1277,24 +1277,31 @@ class LotQt(
         Purchase = Pool().get('purchase.purchase')
         LotQt = Pool().get('lot.qt')
         Lot = Pool().get('lot.lot')
+        Uom = Pool().get('product.uom')
         purchase = lqt.lot_p.line.purchase
         lots = []
         tot_qt = 0
+        for l in vlots:
+            tot_qt += Decimal(str(Uom.compute_qty(
+                l.lot_unit_line, float(l.lot_quantity or 0),
+                lqt.lot_p.line.unit)))
+        tot_qt = round(tot_qt, 5)
         with Transaction().set_context(
                 _purchase_trade_skip_quantity_consistency=True):
-            for l in vlots:
-                lot,qt = lqt.add_physical_lot(l)
-                lots.append(lot)
-                tot_qt += qt
-
-            #create move for lots
-            Purchase._process_shipment([purchase],lots)
-
-            #update LotQt
-            lqt.lot_quantity -= round(tot_qt,5)
+            # Consume the forecast first. Physical lot saves recompute the
+            # virtual lot, so the matching lot.qt must already carry the
+            # target open quantity during the rest of the transaction.
+            lqt.lot_quantity -= tot_qt
             if lqt.lot_quantity < 0:
                 lqt.lot_quantity = 0
             LotQt.save([lqt])
+
+            for l in vlots:
+                lot,qt = lqt.add_physical_lot(l)
+                lots.append(lot)
+
+            #create move for lots
+            Purchase._process_shipment([purchase],lots)
         affected_lines = []
         if lqt.lot_p and lqt.lot_p.line:
             affected_lines.append(lqt.lot_p.line)