diff --git a/pyproject.toml b/pyproject.toml
index 95e707656..bfb24f9c8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,3 +1,14 @@
+# Installing the project installs its dependencies and nothing else:
+# `pip install -e ".[dev]"` gives a contributor every tool the tests use.
+# scripts/ and tests/ run from the checkout, so no package is built from them.
+[build-system]
+requires = ["setuptools>=61"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools]
+packages = []
+py-modules = []
+
 [project]
 name = "retrobios"
 version = "1.0.0"
diff --git a/tests/test_audit_regressions.py b/tests/test_audit_regressions.py
index e6f95068d..3b2bfa674 100644
--- a/tests/test_audit_regressions.py
+++ b/tests/test_audit_regressions.py
@@ -2725,6 +2725,34 @@ class DeclaredDependenciesMatchTheDocumentedWorkflows(unittest.TestCase):
         )
 
 
+class TheProjectInstallsWithPip(unittest.TestCase):
+    """pyproject declared a dev extra that pip could not install: without a
+    [build-system] and an explicit module list, setuptools' flat-layout
+    discovery found scripts/ and tests/ and refused to build."""
+
+    def test_setuptools_discovers_nothing_to_package(self):
+        import importlib.util  # noqa: PLC0415
+
+        if importlib.util.find_spec("setuptools") is None:
+            self.skipTest("setuptools is not installed")
+        program = (
+            "from setuptools.dist import Distribution\n"
+            "from setuptools.config.pyprojecttoml import apply_configuration\n"
+            "dist = apply_configuration(Distribution(), 'pyproject.toml')\n"
+            "dist.set_defaults()\n"
+            "print(sorted(dist.packages or []), sorted(dist.py_modules or []))\n"
+        )
+        done = subprocess.run([sys.executable, "-c", program], cwd=ROOT,
+                              capture_output=True, text=True, check=False)
+        self.assertEqual(done.returncode, 0, done.stderr[-2000:])
+        self.assertEqual(done.stdout.strip(), "[] []")
+        import tomllib  # noqa: PLC0415
+
+        with (ROOT / "pyproject.toml").open("rb") as handle:
+            build = tomllib.load(handle)["build-system"]
+        self.assertEqual(build["build-backend"], "setuptools.build_meta")
+
+
 class ACheckThatCannotAnswerDoesNotPass(unittest.TestCase):
     """Exiting zero says the question was answered and the answer was yes.
 
diff --git a/wiki/testing-guide.md b/wiki/testing-guide.md
index d2c28dbc0..43640fc57 100644
--- a/wiki/testing-guide.md
+++ b/wiki/testing-guide.md
@@ -39,8 +39,9 @@ tests are reported as skipped, so install them before a pull request
 (`pip install "jsonschema[format-nongpl]" markdown`). The installer's
 full-screen tests drive `install.py --tui` on a pseudo-terminal and read the
 screen back with `pyte`, and fuzz the key decoder with `hypothesis`: both skip
-without them (`pip install pyte hypothesis`). No test framework beyond the
-standard library `unittest` module.
+without them (`pip install pyte hypothesis`). `pip install -e ".[dev]"` from the
+checkout installs all of these at once, from the `dev` extra of `pyproject.toml`.
+No test framework beyond the standard library `unittest` module.
 
 ## Modules at a glance