diff --git a/Data/TrieMap/IntMap.hs b/Data/TrieMap/IntMap.hs
--- a/Data/TrieMap/IntMap.hs
+++ b/Data/TrieMap/IntMap.hs
@@ -255,6 +255,7 @@
 
 mapEither :: Sized b -> Sized c -> EitherMap Key (a) (b) (c) ->
 	WordMap a -> (WordMap b, WordMap c)
+mapEither _ _ _ Nil = (Nil, Nil)
 mapEither s1 s2 f (Bin _ p m l r) = case (mapEither s1 s2 f l, mapEither s1 s2 f r) of
 	((lL, lR), (rL, rR)) -> (bin p m lL rL, bin p m lR rR)
 mapEither s1 s2 f (Tip _ kx x) = (singletonMaybe s1 kx *** singletonMaybe s2 kx) (f kx x)
diff --git a/Data/TrieMap/Rep/Instances.hs b/Data/TrieMap/Rep/Instances.hs
--- a/Data/TrieMap/Rep/Instances.hs
+++ b/Data/TrieMap/Rep/Instances.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE FlexibleContexts, UndecidableInstances, TypeFamilies, TypeOperators, TemplateHaskell #-}
+{-# LANGUAGE FlexibleContexts, UndecidableInstances, TypeFamilies, TypeOperators, TemplateHaskell, NPlusKPatterns #-}
 
 module Data.TrieMap.Rep.Instances()  where
 
diff --git a/TrieMap.cabal b/TrieMap.cabal
--- a/TrieMap.cabal
+++ b/TrieMap.cabal
@@ -1,5 +1,5 @@
 name:		     TrieMap
-version:             0.6.2
+version:             0.6.3
 tested-with:	     GHC
 category:            Algorithms
 synopsis:	     Automatic type inference of generalized tries.