diff --git a/nix/checks.nix b/nix/checks.nix
index 2966d0e3..2d5bb1d6 100644
--- a/nix/checks.nix
+++ b/nix/checks.nix
@@ -63,6 +63,17 @@ in
   # per-system eval of nix/docs/default.nix happens once.
   inherit (self.packages.${system}) docs;
 
+  # Frontend build. Builds the `hyperhive-frontend` npm package, whose
+  # fixed-output npm-deps derivation pins `npmDepsHash`
+  # (nix/packages/frontend.nix). No other check exercises that FOD:
+  # `cargo-test` forces `.#assets`, but `assets` carries no frontend
+  # dependency, so without this check a stale `npmDepsHash` after a
+  # `package-lock.json` bump that forgets to recompute it sails through
+  # every PR and only breaks when the host toplevel is built on deploy.
+  # Reusing the already-defined `packages.<system>.frontend` derivation
+  # makes such a hash mismatch a red PR instead of a red main.
+  inherit (self.packages.${system}) frontend;
+
   # `hivectl` CLI reference freshness check. The committed
   # markdown at `docs/tools/hivectl-cli.md` is the rendered
   # output of the hidden `hivectl markdown-docs` subcommand