diff --git a/docs/advanced_topics/customisation/custom_user_models.rst b/docs/advanced_topics/customisation/custom_user_models.rst
index a8405d56a..9650342d3 100644
--- a/docs/advanced_topics/customisation/custom_user_models.rst
+++ b/docs/advanced_topics/customisation/custom_user_models.rst
@@ -7,8 +7,7 @@ Custom user forms example
 This example shows how to add a text field and foreign key field to a custom user model
 and configure Wagtail user forms to allow the fields values to be updated.
 
-Create a custom user model. In this case we extend the ``AbstractUser`` class and add
-two fields. The foreign key references another model (not shown).
+Create a custom user model. This must at minimum inherit from ``AbstractBaseUser`` and ``PermissionsMixin``. In this case we extend the ``AbstractUser`` class and add two fields. The foreign key references another model (not shown).
 
 .. code-block:: python