diff --git a/Dockerfile b/Dockerfile
index 3d27d0a..71ba3b9 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM python:3-buster
+FROM python:3.9-slim-bullseye
 
 ENV PYTHONUNBUFFERED 1
 
diff --git a/tombola/settings/base.py b/tombola/settings/base.py
index 6817057..43a7a73 100644
--- a/tombola/settings/base.py
+++ b/tombola/settings/base.py
@@ -173,3 +173,4 @@ STATIC_URL = '/static/'
 
 ALIAS_VALIDATOR_REGEX = r''
 
+DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'