diff --git a/pkgs/development/haskell-modules/lib.nix b/pkgs/development/haskell-modules/lib.nix
index 8a5ed7d4e94..f5713b6cd20 100644
--- a/pkgs/development/haskell-modules/lib.nix
+++ b/pkgs/development/haskell-modules/lib.nix
@@ -387,7 +387,7 @@ rec {
   #
   # readDirectory : Directory -> HaskellPackageOverrideSet
   readDirectory =
-    directory:
+    { directory }:
 
     self: super:
       let