diff --git a/addons/project/project.py b/addons/project/project.py
index 0851be60e4d..e2eaf51baba 100644
--- a/addons/project/project.py
+++ b/addons/project/project.py
@@ -475,8 +475,20 @@ class task(osv.osv):
             ids = child_ids
         return True
 
+    def _check_dates(self, cr, uid, ids, context=None):
+        if context == None:
+            context = {}
+        obj_task = self.browse(cr, uid, ids[0], context=context)
+        start = obj_task.date_start or False
+        end = obj_task.date_end or False
+        if start and end :
+            if start > end:        
+                return False
+        return True           
+
     _constraints = [
-        (_check_recursion, 'Error ! You cannot create recursive tasks.', ['parent_ids'])
+        (_check_recursion, 'Error ! You cannot create recursive tasks.', ['parent_ids']),
+        (_check_dates, 'Error ! Task end-date must be greater then task start-date', ['date_start','date_end'])
     ]
     #
     # Override view according to the company definition
@@ -540,6 +552,7 @@ class task(osv.osv):
         """
         request = self.pool.get('res.request')
         for task in self.browse(cr, uid, ids, context=context):
+            vals = {}
             project = task.project_id
             if project:
                 # Send request to project manager
@@ -562,7 +575,11 @@ class task(osv.osv):
                             reopen = False
                     if reopen:
                         self.do_reopen(cr, uid, [parent_id.id])
-            self.write(cr, uid, [task.id], {'state': 'done', 'date_end':time.strftime('%Y-%m-%d %H:%M:%S'), 'remaining_hours': 0.0})
+            vals.update({'state': 'done'})
+            vals.update({'remaining_hours': 0.0})
+            if not task.date_end:
+                vals.update({ 'date_end':time.strftime('%Y-%m-%d %H:%M:%S')})
+            self.write(cr, uid, [task.id],vals)
             message = _("The task '%s' is done") % (task.name,)
             self.log(cr, uid, task.id, message)
         return True