diff --git a/pyproject.toml b/pyproject.toml
index f98d644..4d6fa14 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -46,7 +46,7 @@ dependencies = [
 [project.optional-dependencies]
 docs = [
     "enum-tools",
-    "sphinx>=4.0.0,<5",
+    "sphinx>=4.0.0,<9",
     "sphinx-autobuild",
     "sphinx-toolbox",
     "sphinxcontrib_trio",