diff --git a/__init__.py b/__init__.py
index 2a4c038..7f021a3 100644
--- a/__init__.py
+++ b/__init__.py
@@ -11,6 +11,7 @@ def register():
     Pool.register(
         ir.Sequence,
         ir.SequencePeriod,
+        ir.SequenceStrict,
         module='ir_sequence_period', type_='model')
     Pool.register(
         sale.Sale,
diff --git a/ir.py b/ir.py
index ef63985..36b1143 100644
--- a/ir.py
+++ b/ir.py
@@ -3,12 +3,12 @@
 from itertools import izip
 from trytond.model import ModelSQL, ModelView, MatchMixin, fields
 from trytond.pool import PoolMeta, Pool
-from trytond.pyson import Eval, And
+from trytond.pyson import Eval, And, Bool
 from trytond.transaction import Transaction
 from trytond import backend
 from sql import Literal, For
 
-__all__ = ['Sequence', 'SequencePeriod']
+__all__ = ['Sequence', 'SequencePeriod', 'SequenceStrict']
 
 sql_sequence = backend.get('Database').has_sequence()
 
@@ -224,3 +224,17 @@ class SequencePeriod(ModelSQL, ModelView, MatchMixin):
         if not date:
             return False
         return self.start_date <= date <= self.end_date
+
+
+class SequenceStrict:
+    __name__ = 'ir.sequence.strict'
+    __metaclass__ = PoolMeta
+
+    # needed due to both models share form view
+    periods = fields.Function(
+        fields.One2Many('ir.sequence.period', None, 'Periods',
+            states={'invisible': Bool(True)}),
+        'get_periods')
+
+    def get_periods(self, name=None):
+        return []