diff --git a/addons/project_retro_planning/project_retro_planning.py b/addons/project_retro_planning/project_retro_planning.py
index c3bbac6c0cf..e9e0f8483f6 100644
--- a/addons/project_retro_planning/project_retro_planning.py
+++ b/addons/project_retro_planning/project_retro_planning.py
@@ -37,9 +37,12 @@ class project_project(osv.osv):
                 if prj.date_end:
                     d= date(*time.strptime(prj.date_end,'%Y-%m-%d')[:3])
                     for task in prj.tasks:
+                        start_dt = (datetime(*time.strptime(task.date_start,'%Y-%m-%d  %H:%M:%S')[:6])+(c-d)).strftime('%Y-%m-%d %H:%M:%S')
                         if task.date_deadline:
-                            f = (datetime(*time.strptime(task.date_deadline,'%Y-%m-%d  %H:%M:%S')[:6])+(c-d)).strftime('%Y-%m-%d %H:%M:%S')
-                            self.pool.get('project.task').write(cr,uid,task.id,{'date_deadline':f})
+                            deadline_dt = (datetime(*time.strptime(task.date_deadline,'%Y-%m-%d  %H:%M:%S')[:6])+(c-d)).strftime('%Y-%m-%d %H:%M:%S')
+                            self.pool.get('project.task').write(cr,uid,task.id,{'date_start':start_dt, 'date_deadline':deadline_dt})
+                        else:
+                            self.pool.get('project.task').write(cr,uid,task.id,{'date_start':start_dt})
         return super(project_project,self).write(cr, uid, ids,vals, *args, **kwargs)
 
 project_project()