diff --git a/timesheet.py b/timesheet.py
index a153a7df36..2e99544a8b 100644
--- a/timesheet.py
+++ b/timesheet.py
@@ -24,7 +24,8 @@ class TimesheetLine(metaclass=PoolMeta):
     def copy(cls, records, default=None):
         if default is None:
             default = {}
-        default = default.copy()
+        else:
+            default = default.copy()
         default.setdefault('invoice_line', None)
         return super(TimesheetLine, cls).copy(records, default=default)
 
diff --git a/work.py b/work.py
index b6de430a32..aacfad497a 100644
--- a/work.py
+++ b/work.py
@@ -93,7 +93,8 @@ class Work(metaclass=PoolMeta):
     def copy(cls, records, default=None):
         if default is None:
             default = {}
-        default = default.copy()
+        else:
+            default = default.copy()
         default.setdefault('invoice_line', None)
         return super(Work, cls).copy(records, default=default)