diff --git a/pyproject.toml b/pyproject.toml
index 32d1147..6065cf9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -35,7 +35,7 @@ exclude = ["benchmarks", "docs", "tests"]
 [project.optional-dependencies]
 dev = ["PyTemplate[doc,test,lint,type,commit]", "tox"]
 commit = ["pre-commit"]
-doc = ["sphinx", "furo", "sphinx_multiversion"]
+doc = ["sphinx<9.0.0", "furo", "sphinx_multiversion"]
 test = ["pytest", "coverage", "pytest-xdist"]
 lint = ["pylint", "ruff"]
 type = ["mypy"]