diff --git a/example/app/test_msf.py b/example/app/test_msf.py
index 3c73978..4f04d78 100644
--- a/example/app/test_msf.py
+++ b/example/app/test_msf.py
@@ -116,7 +116,17 @@ def test_flatchoices(self):
         self.assertEqual(Book._meta.get_field('published_in').flatchoices, list(PROVINCES + STATES))
 
     def test_named_groups(self):
-        self.assertEqual(Book._meta.published_in.choices, PROVINCES_AND_STATES)
+        # We can't use a single self.assertEqual here, because model subchoices may be lists or tuples
+        # Iterate through the parent choices
+        for book_choices, province_or_state_choice in zip(Book._meta.get_field('published_in').choices, PROVINCES_AND_STATES):
+            parent_book_choice, *book_subchoices = book_choices
+            parent_pors_choice, *pors_subchoices = province_or_state_choice
+            # Check the parent keys
+            self.assertEqual(parent_book_choice, parent_pors_choice)
+            # Iterate through all of the subchoices
+            for book_subchoice, pors_subchoice in zip(book_subchoices, pors_subchoices):
+                # The model subchoices might be tuples, so make sure to convert both to lists
+                self.assertEqual(list(book_subchoice), list(pors_subchoice))
 
     def test_named_groups_form(self):
         form_class = modelform_factory(Book, fields=('published_in',))
diff --git a/example/example/settings.py b/example/example/settings.py
index 9c2754d..74290c4 100644
--- a/example/example/settings.py
+++ b/example/example/settings.py
@@ -40,6 +40,8 @@
     }
 }
 
+DEFAULT_AUTO_FIELD = 'django.db.models.BigAutoField'
+
 # Hosts/domain names that are valid for this site; required if DEBUG is False
 # See https://docs.djangoproject.com/en/1.5/ref/settings/#allowed-hosts
 ALLOWED_HOSTS = ['localhost']
diff --git a/multiselectfield/db/fields.py b/multiselectfield/db/fields.py
index 902cc38..e888047 100644
--- a/multiselectfield/db/fields.py
+++ b/multiselectfield/db/fields.py
@@ -14,6 +14,7 @@
 # You should have received a copy of the GNU Lesser General Public License
 # along with this programe.  If not, see <http://www.gnu.org/licenses/>.
 
+from django import VERSION
 from django.db import models
 from django.utils.text import capfirst
 from django.core import exceptions
@@ -54,14 +55,17 @@ def __init__(self, *args, **kwargs):
         self.max_choices = kwargs.pop('max_choices', None)
         super(MultiSelectField, self).__init__(*args, **kwargs)
         self.max_length = get_max_length(self.choices, self.max_length)
-        self.validators[0] = MaxValueMultiFieldValidator(self.max_length)
+        self.validators.append(MaxValueMultiFieldValidator(self.max_length))
         if self.min_choices is not None:
             self.validators.append(MinChoicesValidator(self.min_choices))
         if self.max_choices is not None:
             self.validators.append(MaxChoicesValidator(self.max_choices))
 
     def _get_flatchoices(self):
-        flat_choices = super(MultiSelectField, self)._get_flatchoices()
+        if VERSION >= (5,):
+            flat_choices = super(MultiSelectField, self).flatchoices
+        else:
+            flat_choices = super(MultiSelectField, self)._get_flatchoices()
 
         class MSFFlatchoices(list):
             # Used to trick django.contrib.admin.utils.display_for_field into