From b3aa88c9b9696f30ee93825b7a865f1fbdd8bf71 Mon Sep 17 00:00:00 2001
From: Jacob Rief <jacob.rief@gmail.com>
Date: Thu, 7 Dec 2023 09:16:57 +0100
Subject: [PATCH] Backport to Django-4.0

---
 formset/collection.py | 2 +-
 setup.py              | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/formset/collection.py b/formset/collection.py
index 4cd3a377..7cda9ae9 100644
--- a/formset/collection.py
+++ b/formset/collection.py
@@ -290,7 +290,7 @@ def validate_unique(self):
         for valid_holders in self.valid_holders:
             for name, holder in valid_holders.items():
                 if isinstance(holder, BaseModelForm):
-                    exclude = holder._get_validation_exclusions().difference(unique_fields)
+                    exclude = set(holder._get_validation_exclusions()).difference(unique_fields)
                     unique_checks, date_checks = holder.instance._get_unique_checks(
                         exclude=exclude,
                         include_meta_constraints=True,
diff --git a/setup.py b/setup.py
index 3a6d5d27..4c3ec637 100644
--- a/setup.py
+++ b/setup.py
@@ -19,6 +19,7 @@
     'Programming Language :: Python :: 3.9',
     'Programming Language :: Python :: 3.10',
     'Programming Language :: Python :: 3.11',
+    'Framework :: Django :: 4.0',
     'Framework :: Django :: 4.1',
     'Framework :: Django :: 4.2',
 ]
@@ -32,7 +33,7 @@
     url='https://github.com/jrief/django-formset',
     packages=find_packages(include=['formset', 'formset.*']),
     install_requires=[
-        'django>=4.1',
+        'django>=4.0',
     ],
     extra_requires={
         'thumbnail': ['Pillow'],