diff --git a/jupyterhub/orm.py b/jupyterhub/orm.py
index 30361a96..4dfd3e1d 100644
--- a/jupyterhub/orm.py
+++ b/jupyterhub/orm.py
@@ -46,7 +46,7 @@ class JSONDict(TypeDecorator):
 
     """
 
-    impl = types.LargeBinary
+    impl = LargeBinary
 
     def process_bind_param(self, value, dialect):
         if value is not None: