diff --git a/Control/Categorical/Functor.hs b/Control/Categorical/Functor.hs
--- a/Control/Categorical/Functor.hs
+++ b/Control/Categorical/Functor.hs
@@ -98,3 +98,6 @@
 
 instance Category s => Functor (Dual s) (NT (->)) s where
     map (Dual f) = NT (. f)
+
+instance Functor s t f => Functor (Dual s) (Dual t) f where
+    map (Dual f) = Dual (map f)
diff --git a/Setup.hs b/Setup.hs
deleted file mode 100644
--- a/Setup.hs
+++ /dev/null
@@ -1,2 +0,0 @@
-import Distribution.Simple
-main = defaultMain
diff --git a/category.cabal b/category.cabal
--- a/category.cabal
+++ b/category.cabal
@@ -1,5 +1,5 @@
 name:                category
-version:             0.2.2.0
+version:             0.2.3.0
 synopsis:            Categorical types and classes
 -- description:         
 license:             BSD3