--- old/Storage/Hashed/Monad.hs	2010-05-07 02:35:26.000000000 -0700
+++ new/Storage/Hashed/Monad.hs	2010-11-20 08:38:57.260551570 -0800
@@ -144,7 +144,7 @@
 maybeFlush = do x <- gets changesize
                 when (x > 100 * 1024 * 1024) $ flush
 
-instance (Monad m, MonadError e m) => TreeRO (TreeMonad m) where
+instance (Monad m, Functor m, MonadError e m) => TreeRO (TreeMonad m) where
     expandTo p =
         do t <- gets tree
            case find t p of