diff --git a/docs/reference/google.auth.compute_engine.rst b/docs/reference/google.auth.compute_engine.rst
index 38785c8..819248c 100644
--- a/docs/reference/google.auth.compute_engine.rst
+++ b/docs/reference/google.auth.compute_engine.rst
@@ -10,5 +10,6 @@
 ----------
 
 .. toctree::
+   :maxdepth: 4
 
    google.auth.compute_engine.credentials
diff --git a/docs/reference/google.auth.crypt.rst b/docs/reference/google.auth.crypt.rst
index be142f4..ff38fa3 100644
--- a/docs/reference/google.auth.crypt.rst
+++ b/docs/reference/google.auth.crypt.rst
@@ -10,6 +10,7 @@
 ----------
 
 .. toctree::
+   :maxdepth: 4
 
    google.auth.crypt.base
    google.auth.crypt.es256
diff --git a/docs/reference/google.auth.rst b/docs/reference/google.auth.rst
index f6ea073..cfcf703 100644
--- a/docs/reference/google.auth.rst
+++ b/docs/reference/google.auth.rst
@@ -10,6 +10,7 @@
 -----------
 
 .. toctree::
+   :maxdepth: 4
 
    google.auth.compute_engine
    google.auth.crypt
@@ -19,6 +20,7 @@
 ----------
 
 .. toctree::
+   :maxdepth: 4
 
    google.auth.app_engine
    google.auth.credentials
diff --git a/docs/reference/google.auth.transport.rst b/docs/reference/google.auth.transport.rst
index 48e2e05..8921863 100644
--- a/docs/reference/google.auth.transport.rst
+++ b/docs/reference/google.auth.transport.rst
@@ -10,7 +10,9 @@
 ----------
 
 .. toctree::
+   :maxdepth: 4
 
    google.auth.transport.grpc
+   google.auth.transport.mtls
    google.auth.transport.requests
    google.auth.transport.urllib3
diff --git a/docs/reference/google.oauth2.rst b/docs/reference/google.oauth2.rst
index 4f1df07..1ac9c73 100644
--- a/docs/reference/google.oauth2.rst
+++ b/docs/reference/google.oauth2.rst
@@ -10,6 +10,7 @@
 ----------
 
 .. toctree::
+   :maxdepth: 4
 
    google.oauth2.credentials
    google.oauth2.id_token
diff --git a/docs/reference/google.rst b/docs/reference/google.rst
index 4b1e085..f122ca1 100644
--- a/docs/reference/google.rst
+++ b/docs/reference/google.rst
@@ -10,6 +10,7 @@
 -----------
 
 .. toctree::
+   :maxdepth: 4
 
    google.auth
    google.oauth2
diff --git a/noxfile.py b/noxfile.py
index bcea1fb..c39f27c 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -64,7 +64,7 @@
     session.run("black", *BLACK_PATHS)
 
 
-@nox.session(python=["2.7", "3.5", "3.6", "3.7"])
+@nox.session(python=["2.7", "3.5", "3.6", "3.7", "3.8"])
 def unit(session):
     session.install(*TEST_DEPENDENCIES)
     session.install(".")
diff --git a/setup.py b/setup.py
index 1f5c686..6a70fca 100644
--- a/setup.py
+++ b/setup.py
@@ -56,6 +56,7 @@
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
         "Development Status :: 5 - Production/Stable",
         "Intended Audience :: Developers",
         "License :: OSI Approved :: Apache Software License",