diff --git a/marconi/storage/mongodb/claims.py b/marconi/storage/mongodb/claims.py
index d24c56d76..04090e89e 100644
--- a/marconi/storage/mongodb/claims.py
+++ b/marconi/storage/mongodb/claims.py
@@ -174,6 +174,12 @@ class ClaimController(storage.ClaimBase):
                              upsert=False, multi=True)
 
         if updated != 0:
+            # NOTE(kgriffs): This extra step is necessary because
+            # in between having gotten a list of active messages
+            # and updating them, some of them may have been
+            # claimed by a parallel request. Therefore, we need
+            # to find out which messages were actually tagged
+            # with the claim ID successfully.
             claim, messages = self.get(queue, oid, project=project)
 
         return (str(oid), messages)
diff --git a/marconi/storage/mongodb/messages.py b/marconi/storage/mongodb/messages.py
index b85dfb82c..31d2bfb54 100644
--- a/marconi/storage/mongodb/messages.py
+++ b/marconi/storage/mongodb/messages.py
@@ -25,6 +25,7 @@ import datetime
 import time
 
 import pymongo.errors
+import pymongo.read_preferences
 
 import marconi.openstack.common.log as logging
 from marconi.openstack.common import timeutils
@@ -339,7 +340,12 @@ class MessageController(storage.MessageBase):
             'p': project,
         }
 
-        msgs = self._col.find(query, sort=[('k', 1)])
+        # NOTE(kgriffs): Claimed messages bust be queried from
+        # the primary to avoid a race condition caused by the
+        # multi-phased "create claim" algorithm.
+        preference = pymongo.read_preferences.ReadPreference.PRIMARY
+        msgs = self._col.find(query, sort=[('k', 1)],
+                              read_preference=preference)
 
         if limit:
             msgs = msgs.limit(limit)