diff --git a/.github/workflows/pull_request.yaml b/.github/workflows/pull_request.yaml
index 8041df5e..6c8e9de1 100644
--- a/.github/workflows/pull_request.yaml
+++ b/.github/workflows/pull_request.yaml
@@ -12,7 +12,13 @@ jobs:
         with:
           extra-conf: |
             experimental-features = no-url-literals
+      - uses: cachix/cachix-action@v10
+        if: ${{ !github.event.pull_request.head.repo.fork }}
+        with:
+          name: ngi
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
       - uses: DeterminateSystems/magic-nix-cache-action@main
+        if: ${{ github.event.pull_request.head.repo.fork }}
         with:
           upstream-cache: https://ngi.cachix.org/
       - id: flake-show-diff