diff --git a/Data/Yoko/TH.hs b/Data/Yoko/TH.hs
--- a/Data/Yoko/TH.hs
+++ b/Data/Yoko/TH.hs
@@ -75,6 +75,7 @@
 import qualified Language.Haskell.TH.SCCs as SCCs
 
 import qualified Data.Yoko.TH.Internal as Int
+import Data.Yoko.TH.Internal (tvbName, peelApp, peelAppAcc, expandSyn)
 
 import Data.Functor.Invariant (invmap, invmap2)
 
@@ -82,6 +83,7 @@
 import qualified Control.Monad.Trans as Trans
 
 import qualified Control.Arrow as Arrow
+import Control.Monad ((<=<))
 
 import Data.Set (Set)
 import qualified Data.Set as Set
@@ -196,10 +198,6 @@
 renameCon f (InfixC fieldL n fieldR) = InfixC fieldL (f n) fieldR
 renameCon f (ForallC tvbs cxt c) = ForallC tvbs cxt $ renameCon f c
 
-tvbName :: TyVarBndr -> Name
-tvbName (PlainTV n) = n
-tvbName (KindedTV n _) = n
-
 tvbKind :: TyVarBndr -> Kind
 tvbKind (PlainTV _) = StarK
 tvbKind (KindedTV _ k) = k
@@ -231,17 +229,11 @@
     where lk = k `div` 2   ;   rk = k - lk
           (l, r) = List.splitAt lk as
 
-peelApp :: Type -> (Type, [Type])
-peelApp = peelAppAcc []
-
-peelAppAcc acc (AppT ty0 ty1) = peelAppAcc (ty1 : acc) ty0
-peelAppAcc acc ty             = (ty, acc)
-
 data FieldRO = FieldRO {repF :: Exp, objF :: Exp}
 
 fieldRO :: [(Int, Mapping)] -> Set Name -> Type -> Q (Type, FieldRO)
 fieldRO maps bg = w' where
-  w' = uncurry w . peelApp
+  w' = uncurry w <=< uncurry expandSyn . peelApp
 
   isRec n = Set.member n bg
 
diff --git a/Data/Yoko/TH/Internal.hs b/Data/Yoko/TH/Internal.hs
--- a/Data/Yoko/TH/Internal.hs
+++ b/Data/Yoko/TH/Internal.hs
@@ -1,5 +1,9 @@
+{-# LANGUAGE ViewPatterns #-}
+
 module Data.Yoko.TH.Internal where
 
+import Data.Maybe (fromMaybe)
+
 import Language.Haskell.TH
 
 
@@ -27,3 +31,41 @@
 dataType2Dec n (DataType tvbs cons) = case cons of
   Left  con  -> NewtypeD [] n tvbs con  []
   Right cons -> DataD    [] n tvbs cons []
+
+
+
+
+tvbName :: TyVarBndr -> Name
+tvbName (PlainTV n) = n
+tvbName (KindedTV n _) = n
+
+
+
+peelApp :: Type -> (Type, [Type])
+peelApp = peelAppAcc []
+
+peelAppAcc acc (AppT ty0 ty1) = peelAppAcc (ty1 : acc) ty0
+peelAppAcc acc ty             = (ty, acc)
+
+
+
+expandSyn :: Type -> [Type] -> Q (Type, [Type])
+expandSyn ty@(ConT n) tys = do
+  i <- reify n
+  case i of
+    TyConI (TySynD _ (map tvbName -> formals) rhs) ->
+      uncurry expandSyn $ peelApp $ msubst (zip formals tys) rhs
+    _ -> return (ty, tys)
+expandSyn ty tys = return (ty, tys)
+
+
+
+msubst :: [(Name, Type)] -> Type -> Type
+msubst sigma = w where
+  w ty@(VarT n) = fromMaybe ty $ lookup n sigma
+  w (ForallT tvbs cxt ty) =
+    ForallT tvbs cxt $ msubst (filter p sigma) ty
+    where p = (`elem` map tvbName tvbs) . fst
+  w (AppT ty1 ty2) = AppT (w ty1) (w ty2)
+  w (SigT ty k) = SigT (w ty) k
+  w ty = ty
diff --git a/yoko.cabal b/yoko.cabal
--- a/yoko.cabal
+++ b/yoko.cabal
@@ -1,5 +1,5 @@
 name: yoko
-version: 0.3.2
+version: 0.3.2.1
 synopsis: Generic Programming with Disbanded Data Types
 
 description: