diff --git a/purchase.py b/purchase.py
index 536df16c84..e0d7757c28 100644
--- a/purchase.py
+++ b/purchase.py
@@ -1424,9 +1424,18 @@ class PurchaseLine(sequence_ordered(), ModelSQL, ModelView):
         elif self.purchase.invoice_method == 'shipment':
             quantity = 0.0
             for move in self.moves:
-                if move.state == 'done':
-                    quantity += Uom.compute_qty(move.uom, move.quantity,
-                        self.unit)
+                if move.state != 'done':
+                    continue
+                qty = Uom.compute_qty(move.uom, move.quantity, self.unit)
+                # Test only against from_location
+                # as it is what matters for purchase
+                src_type = self.from_location.type
+                if (move.from_location.type == src_type
+                        and move.to_location.type != src_type):
+                    quantity += qty
+                elif (move.to_location.type == src_type
+                        and move.from_location.type != src_type):
+                    quantity -= qty
             if self.quantity < 0:
                 quantity *= -1
             return quantity