diff --git a/README.md b/README.md
index 7db1199..5b671a5 100644
--- a/README.md
+++ b/README.md
@@ -1256,8 +1256,15 @@ standard: normalized scripts in `script/` are the entrypoints for the
 development workflow. Ten of the Makefile's seventeen targets are thin
 shims that call them; `build`, `run`, `dev`, `deps`, `clean`, `css` and
 `version` are inline commands with no script behind them, though
-`build` and `version` both take their value from `script/version`. We
-provide:
+`build` and `version` both take their value from `script/version`.
+
+`make check` needs the third-party browser assets in `static/`, which
+are not committed, so run `make bootstrap` (or just `make assets`) once
+after cloning. Without them the tests fail with a message naming that
+remedy. `make check` does not fetch them itself because it must not
+change any files in the repo.
+
+We provide:
 
 - `script/bootstrap` — install all dependencies (idempotent)
 - `script/setup` — make a fresh clone ready for development