diff --git a/edc_sites/admin/site_model_admin_mixin.py b/edc_sites/admin/site_model_admin_mixin.py
index 00a34d4..0ffc90c 100644
--- a/edc_sites/admin/site_model_admin_mixin.py
+++ b/edc_sites/admin/site_model_admin_mixin.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import collections
+from typing import TYPE_CHECKING, Type
 
 from django.contrib import admin
 from django.core.exceptions import FieldError, ObjectDoesNotExist
@@ -10,6 +11,10 @@
 from ..site import sites
 from .list_filters import SiteListFilter
 
+if TYPE_CHECKING:
+    from django.contrib.admin import SimpleListFilter
+
+
 __all__ = ["SiteModelAdminMixin"]
 
 
@@ -35,7 +40,7 @@ def site_name(self, obj=None):
             return obj.site.name
         return f"{site_profile.site.id} {site_profile.description}"
 
-    def get_list_filter(self, request):
+    def get_list_filter(self, request) -> tuple[str | Type[SimpleListFilter], ...]:
         """Insert `SiteListFilter` before field name `created`.
 
         Remove site from the list if user does not have access
diff --git a/edc_sites/modelform_mixins.py b/edc_sites/modelform_mixins.py
index d05e36b..6e296c3 100644
--- a/edc_sites/modelform_mixins.py
+++ b/edc_sites/modelform_mixins.py
@@ -1,11 +1,7 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
-
 from django import forms
-
-if TYPE_CHECKING:
-    from django.contrib.sites.models import Site
+from django.contrib.sites.models import Site
 
 __all__ = ["SiteModelFormMixin"]
 
@@ -32,7 +28,11 @@ def clean(self) -> dict:
 
     @property
     def site(self) -> Site:
-        return self.cleaned_data.get("site") or self.instance.site or self.related_visit.site
+        if related_visit := getattr(self, "related_visit", None):
+            return related_visit.site
+        return (
+            self.cleaned_data.get("site") or self.instance.site or Site.objects.get_current()
+        )
 
     def validate_with_current_site(self) -> None:
         current_site = getattr(self, "current_site", None)