diff --git a/Crypto/Random/Entropy/Windows.hs b/Crypto/Random/Entropy/Windows.hs
index f697eba..9eeb70d 100644
--- a/Crypto/Random/Entropy/Windows.hs
+++ b/Crypto/Random/Entropy/Windows.hs
@@ -9,6 +9,7 @@
 --   Copyright (c) Thomas DuBuisson.
 --
 {-# LANGUAGE ForeignFunctionInterface #-}
+{-# LANGUAGE CPP #-}
 module Crypto.Random.Entropy.Windows
     ( WinCryptoAPI
     ) where