diff --git a/data/registry_model/datatype.py b/data/registry_model/datatype.py
index 6571e61b4..0b72b5fa8 100644
--- a/data/registry_model/datatype.py
+++ b/data/registry_model/datatype.py
@@ -28,7 +28,7 @@ def datatype(name, static_fields):
       if name in static_fields:
         return self._fields[name]
 
-      return None
+      raise AttributeError('Unknown field `%s`' % name)
 
   return DataType
 
diff --git a/data/registry_model/test/test_pre_oci_model.py b/data/registry_model/test/test_pre_oci_model.py
index 78b5ca545..d3047cff1 100644
--- a/data/registry_model/test/test_pre_oci_model.py
+++ b/data/registry_model/test/test_pre_oci_model.py
@@ -64,7 +64,7 @@ def test_lookup_manifests(repo_namespace, repo_name, pre_oci_model):
   found_tag = pre_oci_model.find_matching_tag(repository_ref, ['latest'])
   found_manifest = pre_oci_model.get_manifest_for_tag(found_tag)
   found = pre_oci_model.lookup_manifest_by_digest(repository_ref, found_manifest.digest)
-  assert found.id == found_manifest.id
+  assert found._db_id == found_manifest._db_id
   assert found.digest == found_manifest.digest