diff --git a/pyproject.toml b/pyproject.toml
index 882f1e3e..03c88da0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -84,7 +84,7 @@ optional-dependencies.dev = [
     # use it to lint shell commands in GitHub workflow files.
     "shellcheck-py==0.11.0.1",
     "shfmt-py==3.12.0.2",
-    "sphinx==8.2.3",
+    "sphinx==9.0.1",
     "sphinx-copybutton==0.5.2",
     "sphinx-lint==1.0.2",
     "sphinx-paramlinks==0.6",