diff --git a/suitcase/mongo_normalized/__init__.py b/suitcase/mongo_normalized/__init__.py
index dcd2f8a..e7c1da8 100644
--- a/suitcase/mongo_normalized/__init__.py
+++ b/suitcase/mongo_normalized/__init__.py
@@ -208,7 +208,9 @@ def update(self, name, doc):
                 for field in restricted_fields:
                     if field in old and field in doc:
                         if old[field] != doc[field]:
-                            raise ValueError(
+                            # Allow the removal of restricted fields, but not update
+                            if doc[field] != None:
+                                raise ValueError(
                                 f"Field '{field}' is restricted and cannot be changed."
                             )
                 target_uid_docs = revisions_col.find({"document.uid": doc["uid"]})
@@ -224,7 +226,6 @@ def update(self, name, doc):
         else:
             raise NotImplementedError(
                 f"Updating a {name} document is not currently supported. "
-                f"Only updates to 'start' documents are supported."
             )
 
     def start(self, doc):
diff --git a/suitcase/mongo_normalized/tests/fixtures.py b/suitcase/mongo_normalized/tests/fixtures.py
index 2fca399..7c77189 100644
--- a/suitcase/mongo_normalized/tests/fixtures.py
+++ b/suitcase/mongo_normalized/tests/fixtures.py
@@ -2,6 +2,7 @@
 # intake-bluesky-mongo) to import and reuse this fixtures without importing
 # *all* the fixtures used in conftest and the dependencies that they carry.
 import mongomock
+import pymongo
 import pytest
 import uuid
 
@@ -10,8 +11,8 @@
 def db_factory(request):
     def inner():
         database_name = f'test-{str(uuid.uuid4())}'
-        uri = 'mongodb://localhost:27017/'
-        client = mongomock.MongoClient(uri)
+        uri = 'mongodb://dbroker:secret@localhost:27017/test_database?authSource=admin'
+        client = pymongo.MongoClient(uri, False)
 
         def drop():
             client.drop_database(database_name)