diff --git a/pyproject.toml b/pyproject.toml
index 925204d..0f807be 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -42,3 +42,13 @@ packages = ["src/falsegreen_robot"]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]
+
+[tool.ruff.lint]
+# The lint surface is declared here instead of inherited from whatever ruff
+# happens to default to. It used to be inherited, and ruff 0.16 widened its
+# defaults: with `ruff>=0.5` unpinned, CI went from clean to a wall of findings
+# (UP031, E402, BLE001, I001, SIM114, RUF100) with no commit in between. These
+# four sets are exactly what the repo was already being held to. Adopting a wider
+# set is a deliberate change with its own PR, not something a dependency release
+# decides. Same fix as vinicq/falsegreen#148.
+select = ["E4", "E7", "E9", "F"]