diff --git a/Control/Categorical/Functor.hs b/Control/Categorical/Functor.hs
--- a/Control/Categorical/Functor.hs
+++ b/Control/Categorical/Functor.hs
@@ -101,3 +101,9 @@
 
 instance Functor s t f => Functor (Dual s) (Dual t) f where
     map (Dual f) = Dual (map f)
+
+instance (Category t, Functor s (NT t) f) => Functor (Dual s) (NT (Dual t)) f where
+    map (Dual f) = NT (Dual (nt (map f)))
+
+instance (Category s, Category t, Functor s (NT (Dual t)) f) => Functor s (Dual (NT t)) f where
+    map f = Dual (NT (dual (nt (map f))))
diff --git a/category.cabal b/category.cabal
--- a/category.cabal
+++ b/category.cabal
@@ -1,5 +1,5 @@
 name:                category
-version:             0.2.3.0
+version:             0.2.4.0
 synopsis:            Categorical types and classes
 -- description:         
 license:             BSD3