diff --git a/addons/membership/models/account_invoice.py b/addons/membership/models/account_invoice.py
index 73622ce0fb2..85b158e4959 100644
--- a/addons/membership/models/account_invoice.py
+++ b/addons/membership/models/account_invoice.py
@@ -36,7 +36,7 @@ class AccountInvoiceLine(models.Model):
                 # Product line has changed to a membership product
                 date_from = line.product_id.membership_date_from
                 date_to = line.product_id.membership_date_to
-                if line.invoice_id.date_invoice > date_from and line.invoice_id.date_invoice < date_to:
+                if line.invoice_id.date_invoice > (date_from or '0000-00-00') and line.invoice_id.date_invoice < (date_to or '0000-00-00'):
                     date_from = line.invoice_id.date_invoice
                 MemberLine.create({
                     'partner': line.invoice_id.partner_id.id,
@@ -60,9 +60,9 @@ class AccountInvoiceLine(models.Model):
                 invoice_line.product_id.membership and \
                 not MemberLine.search([('account_invoice_line', '=', invoice_line.id)]):
             # Product line is a membership product
-            date_from = invoice_line.product_id.membership_date_from or '0000-00-00'
-            date_to = invoice_line.product_id.membership_date_to or '0000-00-00'
-            if date_from < (invoice_line.invoice_id.date_invoice or '0000-00-00') < date_to:
+            date_from = invoice_line.product_id.membership_date_from
+            date_to = invoice_line.product_id.membership_date_to
+            if date_from and date_from < (invoice_line.invoice_id.date_invoice or '0000-00-00') < (date_to or '0000-00-00'):
                 date_from = invoice_line.invoice_id.date_invoice
             MemberLine.create({
                 'partner': invoice_line.invoice_id.partner_id.id,
diff --git a/addons/membership/models/partner.py b/addons/membership/models/partner.py
index 89da36bc273..348d4d04dfa 100644
--- a/addons/membership/models/partner.py
+++ b/addons/membership/models/partner.py
@@ -108,7 +108,7 @@ class Partner(models.Model):
             s = 4
             if partner.member_lines:
                 for mline in partner.member_lines:
-                    if mline.date_to >= today and mline.date_from <= today:
+                    if (mline.date_to or '0000-00-00') >= today and (mline.date_from or '0000-00-00') <= today:
                         if mline.account_invoice_line.invoice_id:
                             mstate = mline.account_invoice_line.invoice_id.state
                             if mstate == 'paid':
@@ -126,7 +126,7 @@ class Partner(models.Model):
                                 s = 3
                 if s == 4:
                     for mline in partner.member_lines:
-                        if mline.date_from < today and mline.date_to < today and mline.date_from <= mline.date_to and mline.account_invoice_line and mline.account_invoice_line.invoice_id.state == 'paid':
+                        if (mline.date_from or '0000-00-00') < today and (mline.date_to or '0000-00-00') < today and (mline.date_from or '0000-00-00') <= (mline.date_to or '0000-00-00') and mline.account_invoice_line and mline.account_invoice_line.invoice_id.state == 'paid':
                             s = 5
                         else:
                             s = 6