diff --git a/pkgs/development/libraries/haskell/wai-test/default.nix b/pkgs/development/libraries/haskell/wai-test/default.nix
index 9cae0a85d6c9..7d97fe4b4fe1 100644
--- a/pkgs/development/libraries/haskell/wai-test/default.nix
+++ b/pkgs/development/libraries/haskell/wai-test/default.nix
@@ -12,6 +12,7 @@ cabal.mkDerivation (self: {
     httpTypes HUnit network text transformers wai
   ];
   testDepends = [ hspec wai ];
+  postBuild = ":";
   meta = {
     homepage = "http://www.yesodweb.com/book/web-application-interface";
     description = "Unit test framework (built on HUnit) for WAI applications";