diff --git a/pyproject.toml b/pyproject.toml
index 2f2f56dfb..fe181552b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -33,7 +33,7 @@ dependencies = [
 [project.optional-dependencies]
 doc = [
     "numpydoc==1.5.0",
-    "Sphinx==6.1.3",
+    "Sphinx==5.3.0",
     "sphinx-copybutton==0.5.1",
     "sphinx-notfound-page==0.8.3",
 ]