diff --git a/default.nix b/default.nix
index f85fc0c..945f76d 100644
--- a/default.nix
+++ b/default.nix
@@ -1,6 +1,9 @@
-{ pkgs ? import (fetchTarball {
-  url = "https://github.com/NixOS/nixpkgs/archive/refs/tags/24.05.tar.gz";
-}) {} }:
+{
+  pkgs ? import (fetchTarball {
+    # nixos-unstable rev 2024-12-03
+    url = "https://github.com/NixOS/nixpkgs/archive/55d15ad12a74eb7d4646254e13638ad0c4128776.tar.gz";
+  }) { },
+}:
 
 let
   haskellPackages = pkgs.haskell.packages.ghc948;
diff --git a/shell.nix b/shell.nix
index ddb9d28..fb9d7b7 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,6 +1,9 @@
-{ pkgs ? import (fetchTarball {
-  url = "https://github.com/NixOS/nixpkgs/archive/refs/tags/24.05.tar.gz";
-}) {} }:
+{
+  pkgs ? import (fetchTarball {
+    # nixos-unstable rev 2024-12-03
+    url = "https://github.com/NixOS/nixpkgs/archive/55d15ad12a74eb7d4646254e13638ad0c4128776.tar.gz";
+  }) { },
+}:
 
 let
   haskellator = pkgs.callPackage ./default.nix {};