diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 0caee890b2..2e56e0218e 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -4,9 +4,10 @@ nixCache:
     - "mkdir -p ops/secrets"
     - "cp ${OPS_SECRETS_DEFAULT_NIX} ops/secrets/default.nix"
     - "test -d cache || mkdir cache"
-    - "nix-build ./ci-root.nix --option substituters \"file://$PWD/cache?trusted=1 https://cache.nixos.org s3://lukegb-nix-cache?endpoint=storage.googleapis.com&trusted=1\""
-    - "nix copy --to 'file://cache' ./result"
-    - "nix copy --to 's3://lukegb-nix-cache?endpoint=storage.googleapis.com' ./result"
+    - "test -f cache/nix.closure && nix-store --import < cache/nix.closure"
+    - "nix build -vv -f ./ci-root.nix --substituters \"https://cache.nixos.org s3://lukegb-nix-cache?endpoint=storage.googleapis.com&trusted=1\""
+    - "nix-store --export $(nix-store -qR ./result) > cache/nix.closure"
+    - "nix copy -vv --to 's3://lukegb-nix-cache?endpoint=storage.googleapis.com' ./result"
   cache:
     key: one-key-to-rule-them-all
     paths: