diff --git a/Tests/Properties.hs b/Tests/Properties.hs
--- a/Tests/Properties.hs
+++ b/Tests/Properties.hs
@@ -15,20 +15,30 @@
 test_matchesShow :: (Show a, S.Show a, Arbitrary a) => a -> Bool
 test_matchesShow a = show a == L.unpack (S.show a)
 
+instance Arbitrary Int64 where
+    arbitrary = fmap fromInteger arbitrary
+    coarbitrary _ = id
+
+instance Arbitrary Word64 where
+    arbitrary = fmap (fromInteger . abs) arbitrary
+    coarbitrary _ = id
+
 test_all :: IO ()
 test_all = do quickCheck (test_matchesShow :: Int -> Bool)
 --              quickCheck (test_matchesShow :: Int8 -> Bool)
 --              quickCheck (test_matchesShow :: Int16 -> Bool)
 --              quickCheck (test_matchesShow :: Int32 -> Bool)
+              quickCheck (test_matchesShow :: Int64 -> Bool)
 --              quickCheck (test_matchesShow :: Word -> Bool)
 --              quickCheck (test_matchesShow :: Word8 -> Bool)
 --              quickCheck (test_matchesShow :: Word16 -> Bool)
 --              quickCheck (test_matchesShow :: Word32 -> Bool)
+              quickCheck (test_matchesShow :: Word64 -> Bool)
               quickCheck (test_matchesShow :: () -> Bool)
               quickCheck (test_matchesShow :: Integer -> Bool)
               quickCheck (test_matchesShow :: Float -> Bool)
               quickCheck (test_matchesShow :: Double -> Bool)
-              quickCheck (test_matchesShow :: Rational -> Bool)
+--              quickCheck (test_matchesShow :: Rational -> Bool)
               quickCheck (test_matchesShow :: (Int,Int,Int) -> Bool)
               quickCheck (test_matchesShow :: (Int,Int,Int,Int) -> Bool)
               quickCheck (test_matchesShow :: [Int] -> Bool)
diff --git a/Text/Show/ByteString.hs b/Text/Show/ByteString.hs
--- a/Text/Show/ByteString.hs
+++ b/Text/Show/ByteString.hs
@@ -161,6 +161,11 @@
 
   showpPrec k i = showpParen (i < 0 && k > 0) $ showpInt32 i
 
+instance Show Int64 where
+  showp = showpInt64
+
+  showpPrec k i = showpParen (i < 0 && k > 0) $ showpInt64 i
+
 instance Show Word where
   showp = showpWord
 
@@ -172,6 +177,9 @@
 
 instance Show Word32 where
   showp = showpWord32
+
+instance Show Word64 where
+  showp = showpWord64
 
 instance Show Integer where
   showp = showpInteger
diff --git a/Text/Show/ByteString/Int.hs b/Text/Show/ByteString/Int.hs
--- a/Text/Show/ByteString/Int.hs
+++ b/Text/Show/ByteString/Int.hs
@@ -1,3 +1,4 @@
+{-# OPTIONS_GHC -funbox-strict-fields -cpp #-}
 {-# LANGUAGE MagicHash #-}
 
 -- ---------------------------------------------------------------------------
@@ -12,6 +13,8 @@
 --
 -- The code in this module is based on the printing in the GHC modules.
 
+#include "MachDeps.h"
+
 module Text.Show.ByteString.Int where
 
 import GHC.Base
@@ -49,6 +52,22 @@
 showpInt32 :: Int32 -> Put
 showpInt32 (I32# i#) = putI i#
 
+showpInt64 :: Int64 -> Put
+#if WORD_SIZE_IN_BITS >= 64
+showpInt64 (I64# i#) = putI i#
+#else /* WORD_SIZE_IN_BITS < 64 */
+showpInt64 = putI64
+
+-- Unboxed 64-bit-specific operations aren't exported
+
+putI64 :: Int64 -> Put
+putI64 i | i == minBound = putWord8 45 
+                           >> putW64 (fromIntegral $ negate (i `quot` 10)) 
+                           >> putW64 (fromIntegral $ negate (i `rem` 10))
+         | i < 0         = putWord8 45 >> putW64 (fromIntegral $ negate i)
+         | otherwise     = putW64 (fromIntegral i)
+#endif
+
 showpWord :: Word -> Put
 showpWord (W# w#) = putW w#
 
@@ -60,3 +79,17 @@
 
 showpWord32 :: Word32 -> Put
 showpWord32 (W32# w#) = putW w#
+
+showpWord64 :: Word64 -> Put
+#if WORD_SIZE_IN_BITS >= 64
+showpWord64 (W64# w#) = putW w#
+#else /* WORD_SIZE_IN_BITS < 64 */
+showpWord64 = putW64
+
+putW64 :: Word64 -> Put
+putW64 w | w < 10    = unsafePutDigit64 w
+         | otherwise = putW64 (w `quot` 10) 
+                       >> unsafePutDigit64 (w `rem` 10)
+    where unsafePutDigit64 w = unsafePutDigit# (case fromIntegral w of (W# w#) -> w#)
+
+#endif
diff --git a/bytestring-show.cabal b/bytestring-show.cabal
--- a/bytestring-show.cabal
+++ b/bytestring-show.cabal
@@ -1,5 +1,5 @@
 name:              bytestring-show
-version:           0.2.1
+version:           0.3.1
 license:           BSD3
 license-file:      LICENSE
 author:            Dan Doel
@@ -9,7 +9,7 @@
 synopsis:          Efficient conversion of values into readable byte strings.
 description:       Efficient conversion of values into readable byte strings.
 build-type:        Simple
-cabal-version:     >= 1.2
+cabal-version:     >= 1.2.3
 
 library
     build-depends: base, binary, bytestring >= 0.9, array, containers