diff --git a/diversity.cabal b/diversity.cabal
--- a/diversity.cabal
+++ b/diversity.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                diversity
-version:             0.4.0.0
+version:             0.4.0.1
 synopsis:            Return the diversity at each position for all sequences in a fasta file
 description:         Find the diversity of a collection of entities, mainly for use with fasta sequences. Produces a binary which works on fasta files to find the diversity of any order and rarefaction curves for a sliding window across all positions in the sequences. To analyze just a collection of entities, just use the whole sequences and list flag.
 homepage:            https://github.com/GregorySchwartz/diversity
diff --git a/src/src-lib/Math/Diversity/Diversity.hs b/src/src-lib/Math/Diversity/Diversity.hs
--- a/src/src-lib/Math/Diversity/Diversity.hs
+++ b/src/src-lib/Math/Diversity/Diversity.hs
@@ -23,6 +23,16 @@
 hamming :: String -> String -> Int
 hamming xs ys = length $ filter not $ zipWith (==) xs ys
 
+-- | Fast product division
+productDivision :: Double -> [Integer] -> [Integer] -> Double
+productDivision acc [] []     = acc
+productDivision acc [] (y:ys) = (acc / fromInteger y)
+                              * productDivision acc [] ys
+productDivision acc (x:xs) [] = acc * fromInteger x * productDivision acc xs []
+productDivision acc (x:xs) (y:ys)
+    | x == y    = productDivision acc xs ys
+    | otherwise = (fromInteger x / fromInteger y) * productDivision acc xs ys
+
 -- | Returns the diversity of a list of things
 diversity :: (Ord b) => Double -> [b] -> Double
 diversity order sample
@@ -39,9 +49,10 @@
 -- | Binomial for small or large numbers (slow but works for big numbers,
 -- fast but works for small numbers)
 specialBinomial :: Bool -> Integer -> Integer -> Integer -> Double
-specialBinomial False n_total g n = fromRational
-    $ product [(n_total - g - n + 1)..(n_total - g)]
-    % product [(n_total - n + 1)..n_total]
+specialBinomial False n_total g n = productDivision 1 num den
+  where
+    num = [(n_total - g - n + 1)..(n_total - g)]
+    den = [(n_total - n + 1)..n_total]
 specialBinomial True n_total g n = choose
                                    (fromIntegral n_total - fromIntegral g)
                                    (fromIntegral n)