diff --git a/addons/mrp_operations/mrp_operations.py b/addons/mrp_operations/mrp_operations.py
index 94f1460ca1c..038c1504678 100644
--- a/addons/mrp_operations/mrp_operations.py
+++ b/addons/mrp_operations/mrp_operations.py
@@ -56,14 +56,16 @@ class mrp_production_workcenter_line(osv.osv):
                 res[op.id]=False
         return res
     def _get_date_end(self, cr, uid, ids, field_name, arg, context):
-        res={}
+        res = {}
         for op in self.browse(cr, uid, ids, context=context):
-            d = DateTime.strptime(op.date_planned,'%Y-%m-%d %H:%M:%S')
-            i = self.pool.get('hr.timesheet.group').interval_get(cr, uid, op.workcenter_id.timesheet_id.id or False, d, op.hour or 0.0)
-            if i:
-                res[op.id] = i[-1][1].strftime('%Y-%m-%d %H:%M:%S')
-            else:
-                res[op.id] = op.date_planned
+            res[op.id]= False
+            if op.date_planned:
+                d = DateTime.strptime(op.date_planned,'%Y-%m-%d %H:%M:%S')
+                i = self.pool.get('hr.timesheet.group').interval_get(cr, uid, op.workcenter_id.timesheet_id.id or False, d, op.hour or 0.0)
+                if i:
+                    res[op.id] = i[-1][1].strftime('%Y-%m-%d %H:%M:%S')
+                else:
+                    res[op.id] = op.date_planned
         return res
     _inherit = 'mrp.production.workcenter.line'
     _columns = {