diff --git a/noxfile.py b/noxfile.py
index 8464e4980..57e534890 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -425,13 +425,15 @@ def docs(session):
     )
 
 
-@nox.session(python=DEFAULT_PYTHON_VERSION)
+@nox.session(python="3.9")
 def docfx(session):
     """Build the docfx yaml files for this library."""
 
     session.install("-e", ".")
     session.install(
-        "sphinx==4.0.2", "alabaster", "recommonmark", "gcp-sphinx-docfx-yaml"
+        "gcp-sphinx-docfx-yaml",
+        "alabaster",
+        "recommonmark",
     )
 
     shutil.rmtree(os.path.join("docs", "_build"), ignore_errors=True)