diff --git a/nix/haskell.nix b/nix/haskell.nix
index aa41767f18b..b6c1a78b4c9 100644
--- a/nix/haskell.nix
+++ b/nix/haskell.nix
@@ -44,7 +44,6 @@ let
         packages.cardano-ledger = {
           configureFlags = [ "--ghc-option=-Werror" ];
           components = {
-            all.postInstall = pkgs.lib.mkForce "";
             tests.cardano-ledger-test = {
               preCheck = ''
                 export CARDANO_MAINNET_MIRROR="${cardano-mainnet-mirror}/epochs"
diff --git a/nix/sources.json b/nix/sources.json
index 01b3b0c155e..9404ba41f24 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -5,10 +5,10 @@
         "homepage": "https://input-output-hk.github.io/haskell.nix",
         "owner": "input-output-hk",
         "repo": "haskell.nix",
-        "rev": "35b1ec8cd577bfc5abf7d0325f38aab01de5ed00",
-        "sha256": "0mg18i6g7nxd7qk0kaca6k8dsc3kam21772zlr19k03ff67ws55j",
+        "rev": "f4136211c933b444ab2e0f358abd223929970220",
+        "sha256": "1b9nxzkg29hwczr6pb6a7arxka8z0swzq7b2bqyxqzr4qvpcjlc1",
         "type": "tarball",
-        "url": "https://github.com/input-output-hk/haskell.nix/archive/35b1ec8cd577bfc5abf7d0325f38aab01de5ed00.tar.gz",
+        "url": "https://github.com/input-output-hk/haskell.nix/archive/f4136211c933b444ab2e0f358abd223929970220.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "iohk-nix": {