diff --git a/netbox/extras/tests/test_customfields.py b/netbox/extras/tests/test_customfields.py
index 8da8fcbf1..c3074aa41 100644
--- a/netbox/extras/tests/test_customfields.py
+++ b/netbox/extras/tests/test_customfields.py
@@ -1691,8 +1691,8 @@ class CustomFieldModelFilterTest(TestCase):
     def test_filter_multiselect(self):
         self.assertEqual(self.filterset({'cf_cf10': ['A']}, self.queryset).qs.count(), 1)
         self.assertEqual(self.filterset({'cf_cf10': ['A', 'C']}, self.queryset).qs.count(), 2)
-        self.assertEqual(self.filterset({'cf_cf10': ['null']}, self.queryset).qs.count(), 1)
-        self.assertEqual(self.filterset({'cf_cf10__empty': True}, self.queryset).qs.count(), 1)  # Same as above
+        self.assertEqual(self.filterset({'cf_cf10': ['null']}, self.queryset).qs.count(), 1)  # Contains a literal null
+        self.assertEqual(self.filterset({'cf_cf10__empty': True}, self.queryset).qs.count(), 2)
 
     def test_filter_object(self):
         manufacturer_ids = Manufacturer.objects.values_list('id', flat=True)
diff --git a/netbox/netbox/filtersets.py b/netbox/netbox/filtersets.py
index f24b4e11c..ea24efe48 100644
--- a/netbox/netbox/filtersets.py
+++ b/netbox/netbox/filtersets.py
@@ -29,6 +29,13 @@ __all__ = (
     'OrganizationalModelFilterSet',
 )
 
+STANDARD_LOOKUPS = (
+    'exact',
+    'iexact',
+    'in',
+    'contains',
+)
+
 
 #
 # FilterSets
@@ -159,7 +166,7 @@ class BaseFilterSet(django_filters.FilterSet):
             return {}
 
         # Skip nonstandard lookup expressions
-        if existing_filter.method is not None or existing_filter.lookup_expr not in ['exact', 'iexact', 'in']:
+        if existing_filter.method is not None or existing_filter.lookup_expr not in STANDARD_LOOKUPS:
             return {}
 
         # Choose the lookup expression map based on the filter type