diff --git a/datetime-sb.cabal b/datetime-sb.cabal
index d4740ffb6027c5d03dfd9e3ea7e82734b0cee41b..daca618b28ca40897db5426c094c2a6b01c0a87d 100644
--- a/datetime-sb.cabal
+++ b/datetime-sb.cabal
@@ -21,5 +21,6 @@ library
                      old-locale >= 1.0.0.1,
                      old-time >= 1.0.0.1,
                      time >= 1.1.2.2
+  extensions:       CPP
   exposed-modules:   Data.DateTime
   hs-source-dirs:    src