diff --git a/tox.ini b/tox.ini
index a81cd2b45..8d64b929b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,16 +11,25 @@ commands = pytest --color=yes {posargs}
 
 [testenv:lint]
 description = Lint via pre-commit
-basepython = py39
+base_python = py39
 commands = pre-commit run --all-files
 
 [testenv:mypy]
 description = Typecheck with mypy
-basepython = py39
+base_python = py39
 commands = mypy -p git
 ignore_outcome = true
 
 [testenv:black]
 description = Check style with black
-basepython = py39
+base_python = py39
 commands = black --check --diff git
+
+# Run "tox -e html" for this. It is deliberately excluded from env_list, as
+# unlike the other environments, this one writes outside the .tox/ directory.
+[testenv:html]
+description = Build HTML documentation
+base_python = py39
+deps = -r doc/requirements.txt
+allowlist_externals = make
+commands = make -C doc html