diff --git a/src/BTrees/_datatypes.py b/src/BTrees/_datatypes.py
index 5035144..b59e397 100644
--- a/src/BTrees/_datatypes.py
+++ b/src/BTrees/_datatypes.py
@@ -208,7 +208,20 @@ class O(KeyDataType):
                 # TODO: Shouldn't we only check __cmp__ on Python 2?
                 # Python 3 won't use it.
                 and getattr(item, '__cmp__', None) is None):
-            raise TypeError("Object has default comparison")
+            if isinstance(item, type):
+                # For type objects, check if they have default comparison.
+                # If __lt__ is the default from object, see if metaclass provides __lt__.
+                if getattr(item, '__lt__', None) is object.__lt__:
+                    # Check if metaclass defines __lt__
+                    mt = type(item)
+                    if '__lt__' in mt.__dict__:
+                        # metaclass provides custom comparison, allow
+                        return
+                # Either default __lt__ not overridden by metaclass, or no __lt__ at all
+                raise TypeError("Object has default comparison")
+            else:
+                raise TypeError("Object of class {} has default comparison".format(
+                    item.__class__.__name__))
 
 
     def __call__(self, item):