diff --git a/addons/mrp/models/mrp_workorder.py b/addons/mrp/models/mrp_workorder.py
index 239a97725fd..bdb4f89f6d6 100644
--- a/addons/mrp/models/mrp_workorder.py
+++ b/addons/mrp/models/mrp_workorder.py
@@ -636,10 +636,9 @@ class MrpWorkorder(models.Model):
             vals['leave_id'] = leave.id
             return self.write(vals)
         else:
-            if self.date_planned_start > start_date:
+            if not self.date_planned_start or self.date_planned_start > start_date:
                 vals['date_planned_start'] = start_date
-                if self.duration_expected:
-                    vals['date_planned_finished'] = self._calculate_date_planned_finished(start_date)
+                vals['date_planned_finished'] = self._calculate_date_planned_finished(start_date)
             if self.date_planned_finished and self.date_planned_finished < start_date:
                 vals['date_planned_finished'] = start_date
             return self.with_context(bypass_duration_calculation=True).write(vals)