diff --git a/pkgs/by-name/ni/nix-heuristic-gc/package.nix b/pkgs/by-name/ni/nix-heuristic-gc/package.nix
index 07a43fa9a1d7..4158c0d01421 100644
--- a/pkgs/by-name/ni/nix-heuristic-gc/package.nix
+++ b/pkgs/by-name/ni/nix-heuristic-gc/package.nix
@@ -20,7 +20,7 @@ python3Packages.buildPythonPackage rec {
 
   # NIX_SYSTEM suggested at
   # https://github.com/NixOS/nixpkgs/issues/386184#issuecomment-2692433531
-  NIX_SYSTEM = nixVersions.nixComponents_2_30.nix-store.stdenv.hostPlatform.system;
+  env.NIX_SYSTEM = nixVersions.nixComponents_2_30.nix-store.stdenv.hostPlatform.system;
 
   buildInputs = [
     boost