diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 97da5c3..a31337f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -7,6 +7,10 @@ on:
 
 env:
   nixpkgs_channel: nixpkgs=channel:nixos-23.11
+  oldest_supported_installer: nix-2.8.0
+  # Fetch new versions from the Nix CI run: https://github.com/NixOS/nix/blob/master/.github/workflows/ci.yml
+  # TODO: add pinning upstream or rethink this
+  pinned_installer_hash: zfzfrbb59jsqrfkldwj8drcr9nhhc49k
 
 jobs:
   simple-build:
@@ -99,7 +103,7 @@ jobs:
       with:
         nix_path: ${{ env.nixpkgs_channel }}
         install_options: --tarball-url-prefix https://nixos-nix-install-tests.cachix.org/serve
-        install_url: https://nixos-nix-install-tests.cachix.org/serve/s62m7lc0q0mz2mxxm9q0kkrcg90njzhq/install
+        install_url: https://nixos-nix-install-tests.cachix.org/serve/${{ env.pinned_installer_hash }}/install
     - run: nix-build test.nix
 
   oldest-supported-installer:
@@ -117,7 +121,7 @@ jobs:
       uses: ./
       with:
         nix_path: ${{ env.nixpkgs_channel }}
-        install_url: https://releases.nixos.org/nix/nix-2.8.0/install
+        install_url: https://releases.nixos.org/nix/${{ env.oldest_supported_installer }}/install
     - run: nix-build test.nix
 
   act-support: