diff --git a/docs/release-notes/version-2.9.md b/docs/release-notes/version-2.9.md
index fc64d02ec..264004281 100644
--- a/docs/release-notes/version-2.9.md
+++ b/docs/release-notes/version-2.9.md
@@ -14,6 +14,7 @@
 * [#5206](https://github.com/netbox-community/netbox/issues/5206) - Apply user pagination preferences to all paginated object lists
 * [#5217](https://github.com/netbox-community/netbox/issues/5217) - Prevent erroneous removal of prefetched GenericForeignKey data from tables
 * [#5218](https://github.com/netbox-community/netbox/issues/5218) - Raise validation error if a power port's `allocated_draw` exceeds its `maximum_draw`
+* [#5220](https://github.com/netbox-community/netbox/issues/5220) - Fix API patch request against IP Address endpoint with null assigned_object_type 
 * [#5221](https://github.com/netbox-community/netbox/issues/5221) - Fix bulk component creation for virtual machines
 
 ---
diff --git a/netbox/ipam/api/serializers.py b/netbox/ipam/api/serializers.py
index 6be0b8a42..ea84191f1 100644
--- a/netbox/ipam/api/serializers.py
+++ b/netbox/ipam/api/serializers.py
@@ -219,7 +219,8 @@ class IPAddressSerializer(TaggedObjectSerializer, CustomFieldModelSerializer):
     role = ChoiceField(choices=IPAddressRoleChoices, allow_blank=True, required=False)
     assigned_object_type = ContentTypeField(
         queryset=ContentType.objects.filter(IPADDRESS_ASSIGNMENT_MODELS),
-        required=False
+        required=False,
+        allow_null=True
     )
     assigned_object = serializers.SerializerMethodField(read_only=True)
     nat_inside = NestedIPAddressSerializer(required=False, allow_null=True)