diff --git a/Crypto/PasswordStore.hs b/Crypto/PasswordStore.hs
--- a/Crypto/PasswordStore.hs
+++ b/Crypto/PasswordStore.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE OverloadedStrings, BangPatterns #-}
 -- |
 -- Module      : Crypto.PasswordStore
 -- Copyright   : (c) Peter Scott, 2011
@@ -113,7 +113,8 @@
 -- or more. If the number of rounds specified is 0, the ByteString will be
 -- returned unmodified.
 hashRounds :: ByteString -> Int -> ByteString
-hashRounds bs rounds = (iterate H.hash bs) !! rounds
+hashRounds (!bs) 0 = bs
+hashRounds bs rounds = hashRounds (H.hash bs) (rounds - 1)
 
 -- | Generate a 'Salt' from 128 bits of data from @\/dev\/urandom@, with the
 -- system RNG as a fallback. This is the function used to generate salts by
diff --git a/pwstore-fast.cabal b/pwstore-fast.cabal
--- a/pwstore-fast.cabal
+++ b/pwstore-fast.cabal
@@ -1,5 +1,5 @@
 Name:                pwstore-fast
-Version:             2.1
+Version:             2.2
 Synopsis:            Secure password storage.
 Description:         To store passwords securely, they should be salted,
                      then hashed with a slow hash function. This library