diff --git a/invoice.py b/invoice.py
index db395a2f11..b08873455d 100644
--- a/invoice.py
+++ b/invoice.py
@@ -77,7 +77,8 @@ class Invoice(metaclass=PoolMeta):
     def copy(cls, invoices, default=None):
         if default is None:
             default = {}
-        default = default.copy()
+        else:
+            default = default.copy()
         default.setdefault('purchases', None)
         return super(Invoice, cls).copy(invoices, default=default)
 
diff --git a/purchase.py b/purchase.py
index 5f85532207..3bae9b691c 100644
--- a/purchase.py
+++ b/purchase.py
@@ -630,13 +630,13 @@ class Purchase(Workflow, ModelSQL, ModelView, TaxableMixin):
     def copy(cls, purchases, default=None):
         if default is None:
             default = {}
-        default = default.copy()
-        default['state'] = 'draft'
-        default['number'] = None
-        default['invoice_state'] = 'none'
-        default['invoices_ignored'] = None
-        default['moves'] = None
-        default['shipment_state'] = 'none'
+        else:
+            default = default.copy()
+        default.setdefault('number', None)
+        default.setdefault('invoice_state', 'none')
+        default.setdefault('invoices_ignored', None)
+        default.setdefault('moves', None)
+        default.setdefault('shipment_state', 'none')
         default.setdefault('purchase_date', None)
         return super(Purchase, cls).copy(purchases, default=default)
 
@@ -1530,11 +1530,12 @@ class PurchaseLine(sequence_ordered(), ModelSQL, ModelView):
     def copy(cls, lines, default=None):
         if default is None:
             default = {}
-        default = default.copy()
-        default['moves'] = None
-        default['moves_ignored'] = None
-        default['moves_recreated'] = None
-        default['invoice_lines'] = None
+        else:
+            default = default.copy()
+        default.setdefault('moves', None)
+        default.setdefault('moves_ignored', None)
+        default.setdefault('moves_recreated', None)
+        default.setdefault('invoice_lines', None)
         return super(PurchaseLine, cls).copy(lines, default=default)