diff --git a/src/caosdb/exceptions.py b/src/caosdb/exceptions.py
index 2b4a6f18a92e8a336dfcbcf209d73a71246d0dd9..43dde1851725822d4355bc9cf137746fc6039793 100644
--- a/src/caosdb/exceptions.py
+++ b/src/caosdb/exceptions.py
@@ -141,8 +141,13 @@ class ResourceNotFoundException(ClientErrorException):
         ClientErrorException.__init__(self, msg=msg, status=404, body=None)
 
 
+class MismatchingEntitiesError(CaosDBException):
+    """Mismatching entities were found during container sync."""
+
+
 # ######################### Bad query errors ###########################
 
+
 class BadQueryError(CaosDBException):
     """Base class for query errors that are not transaction errors."""
 
@@ -154,6 +159,7 @@ class QueryNotUniqueError(BadQueryError):
 class EmptyUniqueQueryError(BadQueryError):
     """A unique query or retrieve dound no result."""
 
+
 # ######################### Transaction errors #########################