diff --git a/addons/mass_mailing/models/mailing.py b/addons/mass_mailing/models/mailing.py
index a6cec7fce95..d12930f926f 100644
--- a/addons/mass_mailing/models/mailing.py
+++ b/addons/mass_mailing/models/mailing.py
@@ -40,8 +40,6 @@ class MassMailing(models.Model):
     _name = 'mailing.mailing'
     _description = 'Mass Mailing'
     _inherit = ['mail.thread', 'mail.activity.mixin', 'mail.render.mixin']
-    # number of periods for tracking mail_mail statistics
-    _period_number = 6
     _order = 'sent_date DESC'
     _inherits = {'utm.source': 'source_id'}
     _rec_name = "subject"
diff --git a/addons/project/models/project.py b/addons/project/models/project.py
index b5e6039a5a3..10b91c7092b 100644
--- a/addons/project/models/project.py
+++ b/addons/project/models/project.py
@@ -66,7 +66,6 @@ class Project(models.Model):
     _description = "Project"
     _inherit = ['portal.mixin', 'mail.alias.mixin', 'mail.thread', 'rating.parent.mixin']
     _order = "sequence, name, id"
-    _period_number = 5
     _rating_satisfaction_days = False  # takes all existing ratings
     _check_company_auto = True