diff --git a/src/ZODB/serialize.py b/src/ZODB/serialize.py
index b14b1d033..b4010e840 100644
--- a/src/ZODB/serialize.py
+++ b/src/ZODB/serialize.py
@@ -411,7 +411,7 @@ def serialize(self, obj):
                 meta = klass, newargs()
         elif newargs is None:
             # Pickle format #1.
-            meta = klass
+            meta = klass, None
         else:
             # Pickle format #2.
             meta = klass, newargs()