diff --git a/doc/HISTORY.rst b/doc/HISTORY.rst
index 5b8c7e00f..b0ce12bb7 100644
--- a/doc/HISTORY.rst
+++ b/doc/HISTORY.rst
@@ -1,6 +1,8 @@
 Historical ZODB Changelog
 #########################
 
+- Cleanup of nested mvcc connections could have failed.
+
 3.10.5 (2011-11-19)
 ===================
 
diff --git a/src/ZODB/Connection.py b/src/ZODB/Connection.py
index 6a2bcb906..743e1c582 100644
--- a/src/ZODB/Connection.py
+++ b/src/ZODB/Connection.py
@@ -1085,7 +1085,8 @@ def _resetCache(self):
     def _release_resources(self):
         for c in six.itervalues(self.connections):
             if c._mvcc_storage:
-                c._storage.release()
+                if c._storage is not None:
+                    c._storage.release()
             c._storage = c._normal_storage = None
             c._cache = PickleCache(self, 0, 0)