diff --git a/src/Data/Maybe/Unpacked/Numeric/Int32.hs b/src/Data/Maybe/Unpacked/Numeric/Int32.hs
--- a/src/Data/Maybe/Unpacked/Numeric/Int32.hs
+++ b/src/Data/Maybe/Unpacked/Numeric/Int32.hs
@@ -25,7 +25,6 @@
  
 import Prelude hiding (Maybe,maybe)
 
-import GHC.Base (build)
 import GHC.Exts 
 import GHC.Int (Int32(I32#))
 
diff --git a/src/Data/Maybe/Unpacked/Numeric/Int8.hs b/src/Data/Maybe/Unpacked/Numeric/Int8.hs
--- a/src/Data/Maybe/Unpacked/Numeric/Int8.hs
+++ b/src/Data/Maybe/Unpacked/Numeric/Int8.hs
@@ -25,7 +25,6 @@
 
 import Prelude hiding (Maybe,maybe)
 
-import GHC.Base (build)
 import GHC.Exts 
 import GHC.Int (Int8(I8#))
 
diff --git a/src/Data/Maybe/Unpacked/Numeric/Word128.hs b/src/Data/Maybe/Unpacked/Numeric/Word128.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Maybe/Unpacked/Numeric/Word128.hs
@@ -0,0 +1,122 @@
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE MagicHash #-}
+{-# LANGUAGE UnboxedSums #-}
+{-# LANGUAGE UnboxedTuples #-}
+
+module Data.Maybe.Unpacked.Numeric.Word128
+  ( Maybe(..)
+  , just
+  , nothing
+
+  , maybe
+
+  , isJust
+  , isNothing
+  , fromMaybe
+  , listToMaybe
+  , maybeToList
+  , catMaybes
+  , mapMaybe
+
+  , toBaseMaybe
+  , fromBaseMaybe
+  ) where   
+
+import Prelude hiding (Maybe,maybe)
+
+import Data.WideWord (Word128(..))
+import GHC.Base (build)
+import GHC.Exts (Word#)
+import GHC.Word (Word64(W64#))
+
+import GHC.Read (Read(readPrec))
+import Text.Read (parens, Lexeme(Ident), lexP, (+++))
+import Text.ParserCombinators.ReadPrec (prec, step)
+
+import qualified Prelude as P
+
+data Maybe = Maybe (# (# #) | (# Word#, Word# #) #)
+
+instance Eq Maybe where
+  ma == mb =
+    maybe (isNothing mb)
+          (\a -> maybe False (\b -> a == b) mb) ma
+    
+instance Ord Maybe where
+  compare ma mb = maybe LT (\a -> maybe GT (compare a) mb) ma  
+
+instance Show Maybe where
+  showsPrec p (Maybe m) = case m of
+    (# (# #) | #) -> showString "nothing"
+    (# | (# wa, wb #) #) -> showParen (p > 10)
+      $ showString "just "
+      . showsPrec 11 (Word128 (W64# wa) (W64# wb))
+
+instance Read Maybe where
+  readPrec = parens $ nothingP +++ justP
+    where
+      nothingP = prec 10 $ do
+        Ident "nothing" <- lexP
+        return nothing
+      justP = prec 10 $ do
+        Ident "just" <- lexP
+        a <- step readPrec
+        return (just a)
+
+listToMaybe :: [Word128] -> Maybe
+listToMaybe [] = nothing
+listToMaybe (x:_) = just x
+
+maybeToList :: Maybe -> [Word128]
+maybeToList = maybe [] (: [])
+
+catMaybes :: [Maybe] -> [Word128]
+catMaybes = mapMaybe id
+
+mapMaybe :: (a -> Maybe) -> [a] -> [Word128]
+mapMaybe _ [] = []
+mapMaybe f (a : as) =
+  let ws = mapMaybe f as
+  in maybe ws (: ws) (f a)
+{-# NOINLINE [1] mapMaybe #-}
+
+{-# RULES
+"mapMaybe"     [~1] forall f xs. mapMaybe f xs
+                    = build (\c n -> foldr (mapMaybeFB c f) n xs)
+"mapMaybeList" [1]  forall f. foldr (mapMaybeFB (:) f) [] = mapMaybe f
+  #-}
+
+{-# NOINLINE [0] mapMaybeFB #-}
+mapMaybeFB :: (Word128 -> r -> r) -> (a -> Maybe) -> a -> r -> r
+mapMaybeFB cons f x next = maybe next (flip cons next) (f x)
+
+isNothing :: Maybe -> Bool
+isNothing = maybe True (const False)
+
+isJust :: Maybe -> Bool
+isJust = maybe False (const True)
+
+nothing :: Maybe
+nothing = Maybe (# (# #) | #)
+
+just :: Word128 -> Maybe
+just (Word128 (W64# wa) (W64# wb)) = Maybe (# | (# wa, wb #) #)
+
+fromMaybe :: Word128 -> Maybe -> Word128
+fromMaybe a (Maybe m) = case m of
+  (# (# #) | #) -> a
+  (# | (# wa, wb #) #) -> Word128 (W64# wa) (W64# wb)
+
+maybe :: a -> (Word128 -> a) -> Maybe -> a
+maybe a f (Maybe m) = case m of
+  (# (# #) | #) -> a
+  (# | (# wa, wb #) #) -> f (Word128 (W64# wa) (W64# wb))
+
+toBaseMaybe :: Maybe -> P.Maybe Word128
+toBaseMaybe = maybe P.Nothing P.Just
+
+fromBaseMaybe :: P.Maybe Word128 -> Maybe
+fromBaseMaybe = P.maybe nothing just
+
+
diff --git a/unpacked-maybe-numeric.cabal b/unpacked-maybe-numeric.cabal
--- a/unpacked-maybe-numeric.cabal
+++ b/unpacked-maybe-numeric.cabal
@@ -1,24 +1,25 @@
+cabal-version: 2.2
 name: unpacked-maybe-numeric
-version: 0.1.0.0
+version: 0.1.1.0
 synopsis: maybes of numeric values with fewer indirections
-description: This library provides one `Maybe` type per the usual numeric types:
-             Float, Double, Complex {Float|Double}, Int{|8|16|32|64}, and Word{|8|16|32|64}
-             .
-             All of the numeric types inside the `Maybe` are unboxed, while the `Maybe` value
-             itself is represented as an Unboxed Sum (though for sub-machine-size Int/Word values,
-             the `Maybe` is just a wrapper around the underlying type, with out-of-bounds corresponding
-             to the 'Nothing' value. Thus, the usage of these constructors is unsafe, as this is only
-             checked internally).
+description:
+  This library provides one `Maybe` type per the usual numeric types:
+  Float, Double, Complex {Float|Double}, Int{8|16|32|64}, and Word{8|16|32|64|128}
+  .
+  All of the numeric types inside the `Maybe` are unboxed, while the `Maybe` value
+  itself is represented as an Unboxed Sum. However, for sub-machine-size Int/Word values,
+  the `Maybe` is just a wrapper around the underlying type, with out-of-bounds corresponding
+  to the `Nothing` value. Thus, the use of these constructors is unsafe, as this is only
+  checked internally.
 homepage: https://github.com/andrewthad/unpacked-maybe-numeric#readme
 bug-reports: https://github.com/andrewthad/unpacked-maybe-numeric/issues
 author: Andrew Martin, chessai
 maintainer: andrew.thaddeus@gmail.com, chessai1996@gmail.com
 category: Data
 copyright: 2018 Andrew Martin
-license: BSD3
+license: BSD-3-Clause
 license-file: LICENSE
 build-type: Simple
-cabal-version: >= 1.10
 extra-source-files: README.md
 
 source-repository head
@@ -41,11 +42,12 @@
     Data.Maybe.Unpacked.Numeric.Word16
     Data.Maybe.Unpacked.Numeric.Word32
     Data.Maybe.Unpacked.Numeric.Word64
-  hs-source-dirs:
-      src
+    Data.Maybe.Unpacked.Numeric.Word128
+  hs-source-dirs: src
   build-depends:
-      base >=4.10.1.0 && <5
+    , base >=4.10.1.0 && <5
     , primitive >= 0.6.4
+    , wide-word >= 0.1.0.8 && < 0.2
   ghc-options: -Wall -O2
   default-language: Haskell2010
 
@@ -55,4 +57,8 @@
   type: exitcode-stdio-1.0
   main-is: laws.hs
   hs-source-dirs: test
-  build-depends: base, quickcheck-classes, unpacked-maybe-numeric, QuickCheck
+  build-depends:
+    , QuickCheck
+    , base
+    , quickcheck-classes
+    , unpacked-maybe-numeric