diff --git a/nix/gitlab-ci/default.nix b/nix/gitlab-ci/default.nix
index 47525a76ad..7678ba5ac1 100644
--- a/nix/gitlab-ci/default.nix
+++ b/nix/gitlab-ci/default.nix
@@ -10,7 +10,7 @@ let
       image = "nixos/nix:latest";
       script = [
         "nix run -f ./ third_party.nixpkgs.bash -c ./hack/populate_secrets.sh"
-        "nix build -v -f ./ci-root.nix --argstr system ${system} --substituters \"https://cache.nixos.org/ s3://lukegb-nix-cache?endpoint=storage.googleapis.com&trusted=1\""
+        "nix build -v -f ./ci-root.nix --system ${system} --argstr system ${system} --substituters \"https://cache.nixos.org/ s3://lukegb-nix-cache?endpoint=storage.googleapis.com&trusted=1\""
         "nix copy -v --to 's3://lukegb-nix-cache?endpoint=storage.googleapis.com' ./result"
       ];
       allow_failure = true;
@@ -21,7 +21,7 @@ let
       image = "nixos/nix:latest";
       script = [
         "nix run -f ./ third_party.nixpkgs.bash -c ./hack/populate_secrets.sh"
-        "nix build -v -f ./ci-root.nix --argstr system ${system} --substituters \"https://cache.nixos.org/ s3://lukegb-nix-cache?endpoint=storage.googleapis.com&trusted=1\""
+        "nix build -v -f ./ci-root.nix --system ${system} --argstr system ${system} --substituters \"https://cache.nixos.org/ s3://lukegb-nix-cache?endpoint=storage.googleapis.com&trusted=1\""
         "GOOGLE_APPLICATION_CREDENTIALS=$HOME/sa.json nix run -f ./ go.nix.bcacheup -c bcacheup --cache_url gs://lukegb-nix-cache ./result"
         "cat ./result/other-systemPathJSON > systems.json"
       ];