diff --git a/CHANGELOG.md b/CHANGELOG.md
index 37bb3ed..10632e7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## 0.3.3.0 -- 2020-??-??
 
 * Add `word64PaddedLowerHex` and `word32PaddedLowerHex`
+* Add `word256Array{LE,BE}` and `word256{LE,BE}`
 * Add `word{128,256}Padded{Lower,Upper}Hex`
 
 ## 0.3.2.0 -- 2020-01-20
diff --git a/small-bytearray-builder.cabal b/small-bytearray-builder.cabal
index aba63e2..9227879 100644
--- a/small-bytearray-builder.cabal
+++ b/small-bytearray-builder.cabal
@@ -1,6 +1,6 @@
 cabal-version: 2.2
 name: small-bytearray-builder
-version: 0.3.2.0
+version: 0.3.3.0
 synopsis: Serialize to a small byte arrays
 description:
   This is similar to the builder facilities provided by
diff --git a/src/Data/ByteArray/Builder.hs b/src/Data/ByteArray/Builder.hs
index ee9f0da..af89701 100644
--- a/src/Data/ByteArray/Builder.hs
+++ b/src/Data/ByteArray/Builder.hs
@@ -57,6 +57,7 @@ module Data.ByteArray.Builder
     -- *** One
   , word8
     -- **** Big Endian
+  , word256BE
   , word128BE
   , word64BE
   , word32BE
@@ -65,6 +66,7 @@ module Data.ByteArray.Builder
   , int32BE
   , int16BE
     -- **** Little Endian
+  , word256LE
   , word128LE
   , word64LE
   , word32LE
@@ -79,6 +81,7 @@ module Data.ByteArray.Builder
   , word32ArrayBE
   , word64ArrayBE
   , word128ArrayBE
+  , word256ArrayBE
   , int64ArrayBE
   , int32ArrayBE
   , int16ArrayBE
@@ -87,6 +90,7 @@ module Data.ByteArray.Builder
   , word32ArrayLE
   , word64ArrayLE
   , word128ArrayLE
+  , word256ArrayLE
   , int64ArrayLE
   , int32ArrayLE
   , int16ArrayLE
@@ -119,7 +123,7 @@ import Data.Foldable (foldlM)
 import Data.Int (Int64,Int32,Int16,Int8)
 import Data.Primitive (ByteArray(..),MutableByteArray(..),PrimArray(..))
 import Data.Text.Short (ShortText)
-import Data.WideWord (Word128)
+import Data.WideWord (Word128,Word256)
 import Data.Word (Word64,Word32,Word16,Word8)
 import GHC.ByteOrder (ByteOrder(BigEndian,LittleEndian),targetByteOrder)
 import GHC.Exts (Int(I#),Char(C#),Int#,State#,ByteArray#,(>=#))
@@ -390,6 +394,16 @@ word128ArrayBE src@(PrimArray arr) soff0 slen0 = case targetByteOrder of
   BigEndian -> bytes (Bytes (ByteArray arr) (soff0 * 16) (slen0 * 16))
   LittleEndian -> word128ArraySwap src soff0 slen0
 
+word256ArrayLE :: PrimArray Word256 -> Int -> Int -> Builder
+word256ArrayLE src@(PrimArray arr) soff0 slen0 = case targetByteOrder of
+  LittleEndian -> bytes (Bytes (ByteArray arr) (soff0 * 32) (slen0 * 32))
+  BigEndian -> word256ArraySwap src soff0 slen0
+
+word256ArrayBE :: PrimArray Word256 -> Int -> Int -> Builder
+word256ArrayBE src@(PrimArray arr) soff0 slen0 = case targetByteOrder of
+  BigEndian -> bytes (Bytes (ByteArray arr) (soff0 * 32) (slen0 * 32))
+  LittleEndian -> word256ArraySwap src soff0 slen0
+
 word64ArrayLE :: PrimArray Word64 -> Int -> Int -> Builder
 word64ArrayLE src@(PrimArray arr) soff0 slen0 = case targetByteOrder of
   LittleEndian -> bytes (Bytes (ByteArray arr) (soff0 * 8) (slen0 * 8))
@@ -525,6 +539,28 @@ word128ArraySwap src soff0 slen0 =
       go (soff + 16) send dst (doff + 16)
     else pure doff
 
+word256ArraySwap :: PrimArray Word256 -> Int -> Int -> Builder
+word256ArraySwap src soff0 slen0 =
+  fromFunction (slen0 * 32) (go (soff0 * 32) ((soff0 + slen0) * 32))
+  where
+  -- TODO: Perhaps we could put byteswapping functions to use
+  -- rather than indexing tons of Word8s. This could be done
+  -- both here and in the other swap functions. There are a
+  -- decent number of tests for these array-swapping functions,
+  -- which makes changing this less scary.
+  go :: Int -> Int -> MutableByteArray s -> Int -> ST s Int
+  go !soff !send !dst !doff = if soff < send
+    then do
+      let loop !i
+            | i < 32 = do
+              let v = PM.indexPrimArray (asWord8s src) (soff + i)
+              PM.writeByteArray dst (doff + (31 - i)) v
+              loop (i + 1)
+            | otherwise = pure ()
+      loop 0
+      go (soff + 32) send dst (doff + 32)
+    else pure doff
+
 asWord8s :: PrimArray a -> PrimArray Word8
 asWord8s (PrimArray x) = PrimArray x
 
@@ -766,6 +802,11 @@ int32BE w = fromBounded Nat.constant (Bounded.int32BE w)
 int16BE :: Int16 -> Builder
 int16BE w = fromBounded Nat.constant (Bounded.int16BE w)
 
+-- | Requires exactly 32 bytes. Dump the octets of a 256-bit
+-- word in a little-endian fashion.
+word256LE :: Word256 -> Builder
+word256LE w = fromBounded Nat.constant (Bounded.word256LE w)
+
 -- | Requires exactly 16 bytes. Dump the octets of a 128-bit
 -- word in a little-endian fashion.
 word128LE :: Word128 -> Builder
@@ -786,16 +827,22 @@ word32LE w = fromBounded Nat.constant (Bounded.word32LE w)
 word16LE :: Word16 -> Builder
 word16LE w = fromBounded Nat.constant (Bounded.word16LE w)
 
--- | Requires exactly 8 bytes. Dump the octets of a 64-bit
+
+-- | Requires exactly 32 bytes. Dump the octets of a 256-bit
 -- word in a big-endian fashion.
-word64BE :: Word64 -> Builder
-word64BE w = fromBounded Nat.constant (Bounded.word64BE w)
+word256BE :: Word256 -> Builder
+word256BE w = fromBounded Nat.constant (Bounded.word256BE w)
 
 -- | Requires exactly 16 bytes. Dump the octets of a 128-bit
 -- word in a big-endian fashion.
 word128BE :: Word128 -> Builder
 word128BE w = fromBounded Nat.constant (Bounded.word128BE w)
 
+-- | Requires exactly 8 bytes. Dump the octets of a 64-bit
+-- word in a big-endian fashion.
+word64BE :: Word64 -> Builder
+word64BE w = fromBounded Nat.constant (Bounded.word64BE w)
+
 -- | Requires exactly 4 bytes. Dump the octets of a 32-bit
 -- word in a big-endian fashion.
 word32BE :: Word32 -> Builder
diff --git a/src/Data/ByteArray/Builder/Bounded.hs b/src/Data/ByteArray/Builder/Bounded.hs
index 42a7114..8ecc771 100644
--- a/src/Data/ByteArray/Builder/Bounded.hs
+++ b/src/Data/ByteArray/Builder/Bounded.hs
@@ -66,6 +66,7 @@ module Data.ByteArray.Builder.Bounded
     -- *** One
   , word8
     -- **** Big Endian
+  , word256BE
   , word128BE
   , word64BE
   , word32BE
@@ -74,6 +75,7 @@ module Data.ByteArray.Builder.Bounded
   , int32BE
   , int16BE
     -- **** Little Endian
+  , word256LE
   , word128LE
   , word64LE
   , word32LE
@@ -764,6 +766,12 @@ word128LE (Word128 hi lo) = append (word64LE lo) (word64LE hi)
 word128BE :: Word128 -> Builder 16
 word128BE (Word128 hi lo) = append (word64BE hi) (word64BE lo)
 
+word256LE :: Word256 -> Builder 32
+word256LE (Word256 hi mhi mlo lo) = word64LE lo `append` word64LE mlo `append` word64LE mhi `append` word64LE hi
+
+word256BE :: Word256 -> Builder 32
+word256BE (Word256 hi mhi mlo lo) = word64BE hi `append` word64BE mhi `append` word64BE mlo `append` word64BE lo
+
 -- | Requires exactly 8 bytes. Dump the octets of a 64-bit
 -- word in a little-endian fashion.
 word64LE :: Word64 -> Builder 8
diff --git a/test/Main.hs b/test/Main.hs
index 2af505a..637165b 100644
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -201,6 +201,16 @@ tests = testGroup "Tests"
          in runConcat 1 (foldMap word128BE xs)
             ===
             runConcat 1 (word128ArrayBE ys 0 (Prelude.length xs))
+    , TQC.testProperty "word256ArrayLE" $ \(xs :: [Word256]) ->
+        let ys = Exts.fromList xs :: PrimArray Word256
+         in runConcat 1 (foldMap word256LE xs)
+            ===
+            runConcat 1 (word256ArrayLE ys 0 (Prelude.length xs))
+    , TQC.testProperty "word256ArrayBE" $ \(xs :: [Word256]) ->
+        let ys = Exts.fromList xs :: PrimArray Word256
+         in runConcat 1 (foldMap word256BE xs)
+            ===
+            runConcat 1 (word256ArrayBE ys 0 (Prelude.length xs))
     ]
   , testGroup "alternate"
     [ TQC.testProperty "HexWord64" $ \x y ->