diff --git a/Crypto/Cipher/RC4.hs b/Crypto/Cipher/RC4.hs
--- a/Crypto/Cipher/RC4.hs
+++ b/Crypto/Cipher/RC4.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE ForeignFunctionInterface #-}
+{-# LANGUAGE ForeignFunctionInterface, CPP #-}
 -- |
 -- Module      : Crypto.Cipher.RC4
 -- License     : BSD-style
@@ -6,6 +6,9 @@
 -- Stability   : stable
 -- Portability : Good
 --
+-- Simple implementation of the RC4 stream cipher.
+-- http://en.wikipedia.org/wiki/RC4
+--
 -- Initial FFI implementation by Peter White <peter@janrain.com>
 --
 -- Reorganized and simplified to have an opaque context.
@@ -22,13 +25,19 @@
 import Data.Word
 import Foreign.Ptr
 import Foreign.ForeignPtr
-import System.IO.Unsafe (unsafeDupablePerformIO)
+import System.IO.Unsafe
 import Data.ByteString (ByteString)
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Internal as B
 import Control.Applicative ((<$>))
 
 ----------------------------------------------------------------------
+unsafeDoIO :: IO a -> a
+#if __GLASGOW_HASKELL__ > 704
+unsafeDoIO = unsafeDupablePerformIO
+#else
+unsafeDoIO = unsafePerformIO
+#endif
 
 -- | The encryption context for RC4
 newtype Ctx = Ctx B.ByteString
@@ -60,7 +69,7 @@
 -- adequate otherwise security takes a hit.
 initCtx :: B.ByteString -- ^ The key
         -> Ctx          -- ^ The RC4 context with the key mixed in
-initCtx key = unsafeDupablePerformIO $
+initCtx key = unsafeDoIO $
     Ctx <$> (B.create 264 $ \ctx -> B.useAsCStringLen key $ \(keyPtr,keyLen) -> c_rc4_init (castPtr keyPtr) (fromIntegral keyLen) (castPtr ctx))
 
 -- | generate the next len bytes of the rc4 stream without combining
@@ -72,7 +81,7 @@
 combine :: Ctx                 -- ^ rc4 context
         -> B.ByteString        -- ^ input
         -> (Ctx, B.ByteString) -- ^ new rc4 context, and the output
-combine (Ctx cctx) clearText = unsafeDupablePerformIO $
+combine (Ctx cctx) clearText = unsafeDoIO $
     B.mallocByteString 264 >>= \dctx ->
     B.mallocByteString len >>= \outfptr ->
     withByteStringPtr clearText $ \clearPtr ->
diff --git a/cipher-rc4.cabal b/cipher-rc4.cabal
--- a/cipher-rc4.cabal
+++ b/cipher-rc4.cabal
@@ -1,5 +1,5 @@
 Name:                cipher-rc4
-Version:             0.1.1
+Version:             0.1.2
 Description:         Fast RC4 cipher implementation
 License:             BSD3
 License-file:        LICENSE