diff --git a/account.py b/account.py
index 60d853d280..64dca57111 100644
--- a/account.py
+++ b/account.py
@@ -38,3 +38,12 @@ class InvoiceLine:
             quantity += Uom.compute_qty(stock_move.uom, stock_move.quantity,
                 self.unit)
         return quantity
+
+    @classmethod
+    def copy(cls, lines, default=None):
+        if default is None:
+            default = {}
+        else:
+            default = default.copy()
+        default.setdefault('stock_moves', None)
+        return super(InvoiceLine, cls).copy(lines, default=default)
diff --git a/stock.py b/stock.py
index 1e41bda3d4..14dcf4a2fc 100644
--- a/stock.py
+++ b/stock.py
@@ -23,3 +23,12 @@ class StockMove:
             quantity += Uom.compute_qty(invoice_line.unit,
                 invoice_line.quantity, self.uom)
         return quantity
+
+    @classmethod
+    def copy(cls, moves, default=None):
+        if default is None:
+            default = {}
+        else:
+            default = default.copy()
+        default.setdefault('invoice_lines', None)
+        return super(StockMove, cls).copy(moves, default=default)