diff --git a/rank-product.cabal b/rank-product.cabal
--- a/rank-product.cabal
+++ b/rank-product.cabal
@@ -1,5 +1,5 @@
 name:                rank-product
-version:             0.1.0.3
+version:             0.1.0.4
 synopsis:            Find the rank product of a data set.
 description:         Find the rank product of a data set and get the p-value from a permutation test.
 homepage:            http://github.com/GregorySchwartz/rank-product#readme
diff --git a/src/Statistics/RankProduct.hs b/src/Statistics/RankProduct.hs
--- a/src/Statistics/RankProduct.hs
+++ b/src/Statistics/RankProduct.hs
@@ -36,7 +36,7 @@
 rankProduct :: [Entity] -> [RankProductEntity]
 rankProduct xs =
     fmap ( RankProductEntity
-         . (** (1 / (genericLength . head . fmap unEntity $ xs)))
+         . (** (1 / (genericLength . unEntity . head $ xs)))
          . fromIntegral
          . product
          )
@@ -52,7 +52,7 @@
 prerankProduct xs =
     fmap
         ( RankProductEntity
-        . (** (1 / genericLength xs))
+        . (** (1 / (genericLength . unRankEntity . head $ xs)))
         . fromIntegral
         . product
         . unRankEntity