diff --git a/.envrc b/.envrc
index 1e2885a..2a2dd34 100644
--- a/.envrc
+++ b/.envrc
@@ -2,3 +2,4 @@ if ! has nix_direnv_version || ! nix_direnv_version 2.1.1; then
     source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/2.1.1/direnvrc" "sha256-b6qJ4r34rbE23yWjMqbmu3ia2z4b2wIlZUksBke/ol0="
 fi
 use nix
+watch_file cabal.project wai-middleware-delegate.cabal h8x.nix
diff --git a/default.nix b/default.nix
index 0150db9..ae14438 100644
--- a/default.nix
+++ b/default.nix
@@ -1,24 +1,8 @@
 let
-  # Pin haskell-nix to a recent (as of 2023/07/20) commit
-  h8x-pin = "https://github.com/input-output-hk/haskell.nix/archive/3ae883bb7864ba85c3aab30f8f488b9a7d84afc8.tar.gz";
-  h8x-src = builtins.fetchTarball h8x-pin;
-  h8x = import h8x-src {};
-
-  # Import nixpkgs and pass the haskell.nix provided nixpkgsArgs
-  pkgs = import
-
-    # haskell.nix provides access to the nixpkgs pins which are used by our CI,
-    # hence you will be more likely to get cache hits when using these. But you
-    # can also just use your own, e.g. '<nixpkgs>'.
-
-    h8x.sources.nixpkgs-2305
-
-    # These arguments passed to nixpkgs, include some patches and also the
-    # haskell.nix functionality itself as an overlay.
-
-    h8x.nixpkgsArgs;
-
-in pkgs.haskell-nix.cabalProject {
+  pkgsNix = import ./h8x.nix;
+in
+{ pkgs ? pkgsNix
+} : pkgs.haskell-nix.cabalProject {
   # 'cleanGit' cleans a source directory based on the files known by git
   src = pkgs.haskell-nix.haskellLib.cleanGit {
     name = "wai-middleware-delegate";
@@ -29,5 +13,5 @@ in pkgs.haskell-nix.cabalProject {
   compiler-nix-name = "ghc928";
 
   # Specify the hackage index state
-  index-state = "2023-07-20T00:00:00Z";
+  index-state = "2023-11-24T00:00:00Z";
 }
diff --git a/h8x.nix b/h8x.nix
new file mode 100644
index 0000000..70d571d
--- /dev/null
+++ b/h8x.nix
@@ -0,0 +1,20 @@
+let
+  # Pin haskell-nix to a recent (as of 2023/11/24) commit
+  h8x-commit = "c6e3c91844e91f86cb64015258eed2ed8545d2a9";
+  h8x-pin = "https://github.com/input-output-hk/haskell.nix/archive/${h8x-commit}.tar.gz";
+  h8x-src = builtins.fetchTarball h8x-pin;
+  h8x = import h8x-src {};
+
+in
+  import
+
+    # haskell.nix provides access to the nixpkgs pins which are used by our CI,
+    # hence you will be more likely to get cache hits when using these. But you
+    # can also just use your own, e.g. '<nixpkgs>'.
+
+    h8x.sources.nixpkgs-unstable
+
+    # These arguments passed to nixpkgs, include some patches and also the
+    # haskell.nix functionality itself as an overlay.
+
+    h8x.nixpkgsArgs
diff --git a/shell.nix b/shell.nix
index a11d8ed..7dcdc1e 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,5 +1,5 @@
 let
-  project = import ./default.nix;
+  project = import ./default.nix {};
 in
   project.shellFor {
     # Builds a Hoogle documentation index of all dependencies,
@@ -12,7 +12,7 @@ in
       hlint = "latest"; # Selects the latest version in the hackage.nix snapshot
       haskell-language-server = "latest";
       ghcid = "latest";
-      fourmolu = "latest";
+      fourmolu = "0.14.0.0";
       cabal-fmt = "latest";
     };
     # See overlays/tools.nix for more details