diff --git a/Data/Text/Encoding/Fusion/Common.hs b/Data/Text/Encoding/Fusion/Common.hs
index eedb59df..06807a7f 100644
--- a/Data/Text/Encoding/Fusion/Common.hs
+++ b/Data/Text/Encoding/Fusion/Common.hs
@@ -4,7 +4,8 @@
 -- Module      : Data.Text.Encoding.Fusion.Common
 -- Copyright   : (c) Tom Harper 2008-2009,
 --               (c) Bryan O'Sullivan 2009,
---               (c) Duncan Coutts 2009
+--               (c) Duncan Coutts 2009,
+--               (c) Jasper Van der Jeugt 2011
 --
 -- License     : BSD-style
 -- Maintainer  : bos@serpentine.com, rtomharper@googlemail.com,
@@ -29,7 +30,7 @@ module Data.Text.Encoding.Fusion.Common
 
 import Data.Bits ((.&.))
 import Data.Text.Fusion (Step(..), Stream(..))
-import Data.Text.Fusion.Internal (M(..), S(..))
+import Data.Text.Fusion.Internal (RS(..))
 import Data.Text.UnsafeChar (ord)
 import Data.Text.UnsafeShift (shiftR)
 import Data.Word (Word8)
@@ -37,126 +38,110 @@ import qualified Data.Text.Encoding.Utf8 as U8
 
 -- | /O(n)/ Convert a Stream Char into a UTF-8 encoded Stream Word8.
 restreamUtf8 :: Stream Char -> Stream Word8
-restreamUtf8 (Stream next0 s0 len) =
-    Stream next (S s0 N N N) (len*2)
-    where
-      {-# INLINE next #-}
-      next (S s N N N) = case next0 s of
-                  Done              -> Done
-                  Skip s'           -> Skip (S s' N N N)
-                  Yield x xs
-                      | n <= 0x7F   -> Yield c  (S xs N N N)
-                      | n <= 0x07FF -> Yield a2 (S xs (J b2) N N)
-                      | n <= 0xFFFF -> Yield a3 (S xs (J b3) (J c3) N)
-                      | otherwise   -> Yield a4 (S xs (J b4) (J c4) (J d4))
-                      where
-                        n  = ord x
-                        c  = fromIntegral n
-                        (a2,b2) = U8.ord2 x
-                        (a3,b3,c3) = U8.ord3 x
-                        (a4,b4,c4,d4) = U8.ord4 x
-      next (S s (J x2) N N)   = Yield x2 (S s N N N)
-      next (S s (J x2) x3 N)  = Yield x2 (S s x3 N N)
-      next (S s (J x2) x3 x4) = Yield x2 (S s x3 x4 N)
-      next _ = internalError "restreamUtf8"
+restreamUtf8 (Stream next0 s0 len) = Stream next (RS0 s0) (len * 2)
+  where
+    next (RS0 s) = case next0 s of
+        Done              -> Done
+        Skip s'           -> Skip (RS0 s')
+        Yield x s'
+            | n <= 0x7F   -> Yield c  (RS0 s')
+            | n <= 0x07FF -> Yield a2 (RS1 s' b2)
+            | n <= 0xFFFF -> Yield a3 (RS2 s' b3 c3)
+            | otherwise   -> Yield a4 (RS3 s' b4 c4 d4)
+          where
+            n  = ord x
+            c  = fromIntegral n
+            (a2,b2) = U8.ord2 x
+            (a3,b3,c3) = U8.ord3 x
+            (a4,b4,c4,d4) = U8.ord4 x
+    next (RS1 s x2)       = Yield x2 (RS0 s)
+    next (RS2 s x2 x3)    = Yield x2 (RS1 s x3)
+    next (RS3 s x2 x3 x4) = Yield x2 (RS2 s x3 x4)
+    {-# INLINE next #-}
 {-# INLINE restreamUtf8 #-}
 
 restreamUtf16BE :: Stream Char -> Stream Word8
-restreamUtf16BE (Stream next0 s0 len) =
-    Stream next (S s0 N N N) (len*2)
-    where
-      {-# INLINE next #-}
-      next (S s N N N) = case next0 s of
-          Done -> Done
-          Skip s' -> Skip (S s' N N N)
-          Yield x xs
-              | n < 0x10000 -> Yield (fromIntegral $ n `shiftR` 8) $
-                               S xs (J $ fromIntegral n) N N
-              | otherwise   -> Yield c1 $
-                               S xs (J c2) (J c3) (J c4)
-              where
-                n  = ord x
-                n1 = n - 0x10000
-                c1 = fromIntegral (n1 `shiftR` 18 + 0xD8)
-                c2 = fromIntegral (n1 `shiftR` 10)
-                n2 = n1 .&. 0x3FF
-                c3 = fromIntegral (n2 `shiftR` 8 + 0xDC)
-                c4 = fromIntegral n2
-      next (S s (J x2) N N)   = Yield x2 (S s N N N)
-      next (S s (J x2) x3 N)  = Yield x2 (S s x3 N N)
-      next (S s (J x2) x3 x4) = Yield x2 (S s x3 x4 N)
-      next _ = internalError "restreamUtf16BE"
+restreamUtf16BE (Stream next0 s0 len) = Stream next (RS0 s0) (len * 2)
+  where
+    next (RS0 s) = case next0 s of
+        Done -> Done
+        Skip s' -> Skip (RS0 s')
+        Yield x s'
+            | n < 0x10000 -> Yield (fromIntegral $ n `shiftR` 8) $
+                             RS1 s' (fromIntegral n)
+            | otherwise   -> Yield c1 $ RS3 s' c2 c3 c4
+            where
+              n  = ord x
+              n1 = n - 0x10000
+              c1 = fromIntegral (n1 `shiftR` 18 + 0xD8)
+              c2 = fromIntegral (n1 `shiftR` 10)
+              n2 = n1 .&. 0x3FF
+              c3 = fromIntegral (n2 `shiftR` 8 + 0xDC)
+              c4 = fromIntegral n2
+    next (RS1 s x2)       = Yield x2 (RS0 s)
+    next (RS2 s x2 x3)    = Yield x2 (RS1 s x3)
+    next (RS3 s x2 x3 x4) = Yield x2 (RS2 s x3 x4)
+    {-# INLINE next #-}
 {-# INLINE restreamUtf16BE #-}
 
 restreamUtf16LE :: Stream Char -> Stream Word8
-restreamUtf16LE (Stream next0 s0 len) =
-    Stream next (S s0 N N N) (len*2)
-    where
-      {-# INLINE next #-}
-      next (S s N N N) = case next0 s of
-          Done -> Done
-          Skip s' -> Skip (S s' N N N)
-          Yield x xs
-              | n < 0x10000 -> Yield (fromIntegral n) $
-                               S xs (J (fromIntegral $ shiftR n 8)) N N
-              | otherwise   -> Yield c1 $
-                               S xs (J c2) (J c3) (J c4)
-              where
-                n  = ord x
-                n1 = n - 0x10000
-                c2 = fromIntegral (shiftR n1 18 + 0xD8)
-                c1 = fromIntegral (shiftR n1 10)
-                n2 = n1 .&. 0x3FF
-                c4 = fromIntegral (shiftR n2 8 + 0xDC)
-                c3 = fromIntegral n2
-      next (S s (J x2) N N)   = Yield x2 (S s N N N)
-      next (S s (J x2) x3 N)  = Yield x2 (S s x3 N N)
-      next (S s (J x2) x3 x4) = Yield x2 (S s x3 x4 N)
-      next _ = internalError "restreamUtf16LE"
+restreamUtf16LE (Stream next0 s0 len) = Stream next (RS0 s0) (len * 2)
+  where
+    next (RS0 s) = case next0 s of
+        Done -> Done
+        Skip s' -> Skip (RS0 s')
+        Yield x s'
+            | n < 0x10000 -> Yield (fromIntegral n) $
+                             RS1 s' (fromIntegral $ shiftR n 8)
+            | otherwise   -> Yield c1 $ RS3 s' c2 c3 c4
+          where
+            n  = ord x
+            n1 = n - 0x10000
+            c2 = fromIntegral (shiftR n1 18 + 0xD8)
+            c1 = fromIntegral (shiftR n1 10)
+            n2 = n1 .&. 0x3FF
+            c4 = fromIntegral (shiftR n2 8 + 0xDC)
+            c3 = fromIntegral n2
+    next (RS1 s x2)       = Yield x2 (RS0 s)
+    next (RS2 s x2 x3)    = Yield x2 (RS1 s x3)
+    next (RS3 s x2 x3 x4) = Yield x2 (RS2 s x3 x4)
+    {-# INLINE next #-}
 {-# INLINE restreamUtf16LE #-}
 
 restreamUtf32BE :: Stream Char -> Stream Word8
-restreamUtf32BE (Stream next0 s0 len) =
-    Stream next (S s0 N N N) (len*2)
-    where
-    {-# INLINE next #-}
-    next (S s N N N) = case next0 s of
+restreamUtf32BE (Stream next0 s0 len) = Stream next (RS0 s0) (len * 2)
+  where
+    next (RS0 s) = case next0 s of
         Done       -> Done
-        Skip s'    -> Skip (S s' N N N)
-        Yield x xs -> Yield c1 (S xs (J c2) (J c3) (J c4))
+        Skip s'    -> Skip (RS0 s')
+        Yield x s' -> Yield c1 (RS3 s' c2 c3 c4)
           where
             n  = ord x
             c1 = fromIntegral $ shiftR n 24
             c2 = fromIntegral $ shiftR n 16
             c3 = fromIntegral $ shiftR n 8
             c4 = fromIntegral n
-    next (S s (J x2) N N) = Yield x2 (S s N N N)
-    next (S s (J x2) x3 N)      = Yield x2 (S s x3 N N)
-    next (S s (J x2) x3 x4)           = Yield x2 (S s x3 x4 N)
-    next _ = internalError "restreamUtf32BE"
+    next (RS1 s x2)       = Yield x2 (RS0 s)
+    next (RS2 s x2 x3)    = Yield x2 (RS1 s x3)
+    next (RS3 s x2 x3 x4) = Yield x2 (RS2 s x3 x4)
+    {-# INLINE next #-}
 {-# INLINE restreamUtf32BE #-}
 
 restreamUtf32LE :: Stream Char -> Stream Word8
-restreamUtf32LE (Stream next0 s0 len) =
-    Stream next (S s0 N N N) (len*2)
-    where
-    {-# INLINE next #-}
-    next (S s N N N) = case next0 s of
+restreamUtf32LE (Stream next0 s0 len) = Stream next (RS0 s0) (len * 2)
+  where
+    next (RS0 s) = case next0 s of
         Done       -> Done
-        Skip s'    -> Skip (S s' N N N)
-        Yield x xs -> Yield c1 (S xs (J c2) (J c3) (J c4))
+        Skip s'    -> Skip (RS0 s')
+        Yield x s' -> Yield c1 (RS3 s' c2 c3 c4)
           where
             n  = ord x
             c4 = fromIntegral $ shiftR n 24
             c3 = fromIntegral $ shiftR n 16
             c2 = fromIntegral $ shiftR n 8
             c1 = fromIntegral n
-    next (S s (J x2) N N)   = Yield x2 (S s N N N)
-    next (S s (J x2) x3 N)  = Yield x2 (S s x3 N N)
-    next (S s (J x2) x3 x4) = Yield x2 (S s x3 x4 N)
-    next _ = internalError "restreamUtf32LE"
+    next (RS1 s x2)       = Yield x2 (RS0 s)
+    next (RS2 s x2 x3)    = Yield x2 (RS1 s x3)
+    next (RS3 s x2 x3 x4) = Yield x2 (RS2 s x3 x4)
+    {-# INLINE next #-}
 {-# INLINE restreamUtf32LE #-}
-
-internalError :: String -> a
-internalError func =
-    error $ "Data.Text.Encoding.Fusion.Common." ++ func ++ ": internal error"
diff --git a/Data/Text/Fusion/Internal.hs b/Data/Text/Fusion/Internal.hs
index a5920273..e28d7a82 100644
--- a/Data/Text/Fusion/Internal.hs
+++ b/Data/Text/Fusion/Internal.hs
@@ -3,7 +3,8 @@
 -- Module      : Data.Text.Fusion.Internal
 -- Copyright   : (c) Tom Harper 2008-2009,
 --               (c) Bryan O'Sullivan 2009,
---               (c) Duncan Coutts 2009
+--               (c) Duncan Coutts 2009,
+--               (c) Jasper Van der Jeugt 2011
 --
 -- License     : BSD-style
 -- Maintainer  : bos@serpentine.com, rtomharper@googlemail.com,
@@ -19,7 +20,7 @@ module Data.Text.Fusion.Internal
     , M(..)
     , M8
     , PairS(..)
-    , S(..)
+    , RS(..)
     , Step(..)
     , Stream(..)
     , Switch(..)
@@ -39,7 +40,11 @@ data M a = N
 type M8 = M Word8
 
 -- Restreaming state.
-data S s = S !s !M8 !M8 !M8
+data RS s
+    = RS0 !s
+    | RS1 !s {-# UNPACK #-} !Word8
+    | RS2 !s {-# UNPACK #-} !Word8 {-# UNPACK #-} !Word8
+    | RS3 !s {-# UNPACK #-} !Word8 {-# UNPACK #-} !Word8 {-# UNPACK #-} !Word8
 
 infixl 2 :*:
 data PairS a b = !a :*: !b