diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Revision history for wide-word
 
+## 0.1.0.2  -- 2017-02-08
+
+* Add NFData instances for Word128 and Int128.
+
 ## 0.1.0.1  -- 2017-01-29
 
 * Int128: Fix flakey rewrite rules.
diff --git a/Data/WideWord/Int128.hs b/Data/WideWord/Int128.hs
--- a/Data/WideWord/Int128.hs
+++ b/Data/WideWord/Int128.hs
@@ -29,6 +29,8 @@
   , zeroInt128
   ) where
 
+import Control.DeepSeq (NFData (..))
+
 import Data.Bits (Bits (..), FiniteBits (..), shiftL)
 
 import Data.WideWord.Word128
@@ -137,6 +139,9 @@
   peekElemOff = peekElemOff128
   poke = poke128
   pokeElemOff = pokeElemOff128
+
+instance NFData Int128 where
+  rnf (Int128 a1 a0) = rnf a1 `seq` rnf a0
 
 -- -----------------------------------------------------------------------------
 -- Rewrite rules.
diff --git a/Data/WideWord/Word128.hs b/Data/WideWord/Word128.hs
--- a/Data/WideWord/Word128.hs
+++ b/Data/WideWord/Word128.hs
@@ -28,6 +28,8 @@
   , zeroWord128
   ) where
 
+import Control.DeepSeq (NFData (..))
+
 import Data.Bits (Bits (..), FiniteBits (..), shiftL)
 
 import Foreign.Ptr (Ptr, castPtr)
@@ -134,6 +136,9 @@
   peekElemOff = peekElemOff128
   poke = poke128
   pokeElemOff = pokeElemOff128
+
+instance NFData Word128 where
+  rnf (Word128 a1 a0) = rnf a1 `seq` rnf a0
 
 -- -----------------------------------------------------------------------------
 -- Rewrite rules.
diff --git a/wide-word.cabal b/wide-word.cabal
--- a/wide-word.cabal
+++ b/wide-word.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                wide-word
-version:             0.1.0.1
+version:             0.1.0.2
 synopsis:            Data types for large but fixed width signed and unsigned integers
 description:
   A library to provide data types for large (ie > 64 bits) but fixed width signed
@@ -36,6 +36,7 @@
                      , Data.WideWord.Int128
 
   build-depends:       base                          >= 4.8         && < 5.0
+                     , deepseq                       >= 1.3         && < 1.5
                      , ghc-prim
 
 test-suite test