diff --git a/Crypto/Cipher/Blowfish/Primitive.hs b/Crypto/Cipher/Blowfish/Primitive.hs
index f2b8cd8..6e1af82 100644
--- a/Crypto/Cipher/Blowfish/Primitive.hs
+++ b/Crypto/Cipher/Blowfish/Primitive.hs
@@ -18,10 +18,9 @@ module Crypto.Cipher.Blowfish.Primitive
     , decrypt
     ) where
 
-import Control.Monad (forM_)
+import Control.Monad (forM_, when)
 import Data.Bits
 import Data.Word
-import qualified Data.ByteString as B
 
 import Crypto.Error
 import Crypto.Internal.Compat
@@ -53,23 +52,9 @@ cipher ctx b
 initBlowfish :: ByteArray key => key -> CryptoFailable Context
 initBlowfish key
     | len > (448 `div` 8) = CryptoFailed $ CryptoError_KeySizeInvalid
-    | len == 0            = keyFromByteString (B.replicate (18*4) 0)
-    | otherwise           = keyFromByteString . B.pack . take (18*4) . cycle . B.unpack . byteArrayToBS $ key
+    | otherwise           = CryptoPassed $ makeKeySchedule key
   where len = byteArrayLength key
 
-keyFromByteString :: B.ByteString -> CryptoFailable Context
-keyFromByteString k
-    | B.length k /= (18 * 4) = CryptoFailed CryptoError_KeySizeInvalid
-    | otherwise              = CryptoPassed . makeKeySchedule . w8tow32 . B.unpack $ k
-  where
-    w8tow32 :: [Word8] -> [Word32]
-    w8tow32 [] = []
-    w8tow32 (a:b:c:d:xs) = ( (fromIntegral a `shiftL` 24) .|.
-                             (fromIntegral b `shiftL` 16) .|.
-                             (fromIntegral c `shiftL`  8) .|.
-                             (fromIntegral d) ) : w8tow32 xs
-    w8tow32 _ = error $ "internal error: Crypto.Cipher.Blowfish:keyFromByteString"
-
 coreCrypto :: Context -> Word64 -> Word64
 coreCrypto (BF p s0 s1 s2 s3) input = doRound input 0
   where
@@ -91,11 +76,21 @@ coreCrypto (BF p s0 s1 s2 s3) input = doRound input 0
               d = s3 (fromIntegral $ t .&. 0xff)
            in fromIntegral (((a + b) `xor` c) + d) `shiftL` 32
 
-makeKeySchedule :: [Word32] -> Context
+makeKeySchedule :: ByteArray key => key -> Context
 makeKeySchedule key =
     let v = unsafeDoIO $ do
+              let len = byteArrayLength key
               mv <- createKeySchedule
-              forM_ (zip key [0..17]) $ \(k, i) -> mutableArrayWriteXor32 mv i k
+              when (len > 0) $ forM_ [0..17] $ \i -> do
+                    let a = byteArrayIndex key ((i * 4 + 0) `mod` len)
+                        b = byteArrayIndex key ((i * 4 + 1) `mod` len)
+                        c = byteArrayIndex key ((i * 4 + 2) `mod` len)
+                        d = byteArrayIndex key ((i * 4 + 3) `mod` len)
+                        k = (fromIntegral a `shiftL` 24) .|.
+                            (fromIntegral b `shiftL` 16) .|.
+                            (fromIntegral c `shiftL`  8) .|.
+                            (fromIntegral d)
+                    mutableArrayWriteXor32 mv i k
               prepare mv
               mutableArray32Freeze mv
      in BF (\i -> arrayRead32 v i)