diff --git a/radicale_odoo_storage/__init__.py b/radicale_odoo_storage/__init__.py
index 150ca43..86cc5a8 100644
--- a/radicale_odoo_storage/__init__.py
+++ b/radicale_odoo_storage/__init__.py
@@ -339,5 +339,7 @@ class Collection(BaseCollection):
     def last_modified(self):
         """ Return last modified """
         last = self.odoo.env[self.odoo_model].search([], limit=1, order='write_date desc')
-        last_fields = self.odoo.execute(self.odoo_model, 'read', last, ['write_date'])[0]
-        return str(last_fields['write_date'])
+        if last:
+            last_fields = self.odoo.execute(self.odoo_model, 'read', last, ['write_date'])[0]
+            return str(last_fields['write_date'])
+        return '1970-01-01 00:00:00'