diff --git a/objective.cabal b/objective.cabal
--- a/objective.cabal
+++ b/objective.cabal
@@ -1,8 +1,5 @@
--- Initial objective.cabal generated by cabal init.  For further 
--- documentation, see http://haskell.org/cabal/users-guide/
-
 name:                objective
-version:             0.5.2
+version:             0.5.2.1
 synopsis:            Extensible objects
 description:         Stateful effect transducer
 homepage:            https://github.com/fumieval/objective
@@ -10,7 +7,7 @@
 license-file:        LICENSE
 author:              Fumiaki Kinoshita
 maintainer:          Fumiaki Kinoshita <fumiexcel@gmail.com>
--- copyright:           
+copyright:           Copyright (c) 2014 Fumiaki Kinoshita
 category:            Control
 build-type:          Simple
 extra-source-files:
diff --git a/src/Control/Monad/Objective/Class.hs b/src/Control/Monad/Objective/Class.hs
--- a/src/Control/Monad/Objective/Class.hs
+++ b/src/Control/Monad/Objective/Class.hs
@@ -23,10 +23,11 @@
 
 import Control.Monad
 import Control.Elevator
+import Control.Monad.Trans.State.Strict
 
 type Instance' e m = Instance e m m
 
-class Monad m => MonadObjective m where
+class (Tower m, Monad m) => MonadObjective m where
   data Instance (e :: * -> *) (n :: * -> *) m
   -- | Send a message to the pointed one.
   invoke :: Monad n => Instance e n m -> e a -> m (n (m a))
@@ -39,6 +40,7 @@
   , MonadObjective m
   , Elevate m f) => Instance e n m -> e a -> f a
 a .- e = elevate $ invoke a e >>= join . elevate
+{-# INLINE (.-) #-}
 
 infix 3 .-
 
@@ -49,5 +51,13 @@
   , MonadObjective m
   , Elevate m g) => Instance f n m -> e a -> g a
 a .^ e = a .- elevate e
+{-# INLINE (.^) #-}
 
 infix 3 .^
+
+-- | Specialized (.^) for StateT
+(.&) :: (MonadObjective m, Elevate (StateT s m) e, Monad n, Elevate n m, Elevate m f) => Instance e n m -> StateT s m a -> f a
+(.&) = (.^)
+{-# INLINE (.&) #-}
+infix 3 .&
+