diff --git a/src/Language/Haskell/TH/TypeSub.hs b/src/Language/Haskell/TH/TypeSub.hs
--- a/src/Language/Haskell/TH/TypeSub.hs
+++ b/src/Language/Haskell/TH/TypeSub.hs
@@ -113,7 +113,7 @@
 
 update_ty_vars :: Dec -> Dec 
 update_ty_vars (TySynD n _ t) = (TySynD n (make_ty_vars t) t)
-update_ty_vars dec = set_ty_vars dec $ concatMap make_ty_vars $ 
+update_ty_vars dec = set_ty_vars dec $ nub $ concatMap make_ty_vars $ 
     concatMap (get_con_types) $ get_cons dec
 
     
diff --git a/type-sub-th.cabal b/type-sub-th.cabal
--- a/type-sub-th.cabal
+++ b/type-sub-th.cabal
@@ -7,7 +7,7 @@
 -- The package version. See the Haskell package versioning policy
 -- (http://www.haskell.org/haskellwiki/Package_versioning_policy) for
 -- standards guiding when and how versions should be incremented.
-Version:             0.1.0.4
+Version:             0.1.0.5
 
 homepage: http://github.com/jfischoff/type-sub-th