diff --git a/marconi/queues/storage/mongodb/claims.py b/marconi/queues/storage/mongodb/claims.py
index 073ebf29c..5c4a1f433 100644
--- a/marconi/queues/storage/mongodb/claims.py
+++ b/marconi/queues/storage/mongodb/claims.py
@@ -151,15 +151,19 @@ class ClaimController(storage.ClaimBase):
 
         now = timeutils.utcnow_ts()
 
-        # Set claim field for messages in ids
+        # NOTE(kgriffs): Set the claim field for
+        # the active message batch, while also
+        # filtering out any messages that happened
+        # to get claimed just now by one or more
+        # parallel requests.
+        #
+        # Filtering by just 'c.e' works because
+        # new messages have that field initialized
+        # to the current time when the message is
+        # posted. There is no need to check whether
+        # 'c' exists or 'c.id' is None.
         updated = msg_ctrl._col.update({'_id': {'$in': ids},
-                                        '$or': [
-                                            {'c.id': None},
-                                            {
-                                                'c.id': {'$ne': None},
-                                                'c.e': {'$lte': now}
-                                            }
-                                        ]},
+                                        'c.e': {'$lte': now}},
                                        {'$set': {'c': meta}}, upsert=False,
                                        multi=True)['n']