diff --git a/line.py b/line.py
index 86a5dd730d..72eda4c3b9 100644
--- a/line.py
+++ b/line.py
@@ -137,6 +137,15 @@ class Line(ModelSQL, ModelView):
                 gettext('timesheet.msg_line_duration_positive',
                     line=self.rec_name))
 
+    @classmethod
+    def copy(cls, lines, default=None):
+        if default is not None:
+            default = default.copy()
+        else:
+            default = {}
+        default.setdefault('uuid')
+        return super().copy(lines, default=default)
+
     @property
     def hours(self):
         return self.duration.total_seconds() / 60 / 60