diff --git a/lib/bb/persist_data.py b/lib/bb/persist_data.py
index 9e20a837..ce84a158 100644
--- a/lib/bb/persist_data.py
+++ b/lib/bb/persist_data.py
@@ -208,7 +208,7 @@ class SQLTable(collections.abc.MutableMapping):
 
     def __lt__(self, other):
         if not isinstance(other, Mapping):
-            raise NotImplemented
+            raise NotImplementedError()
 
         return len(self) < len(other)