diff --git a/noxfile.py b/noxfile.py
index 50ae41bf..0fb1e4a0 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -29,34 +29,35 @@
 if os.path.exists("samples"):
     BLACK_PATHS.append("samples")
 
+DEFAULT_PYTHON_VERSION = "3.8"
 
-@nox.session(python="3.7")
+# Error if a python version is missing
+nox.options.error_on_missing_interpreters = True
+
+
+@nox.session(python=DEFAULT_PYTHON_VERSION)
 def lint(session):
     """Run linters.
 
     Returns a failure if the linters find linting errors or sufficiently
     serious code quality issues.
     """
-    session.install("flake8", BLACK_VERSION)
+    session.install("flake8", BLACK_VERSION, "click<8.1")
     session.run("black", "--check", *BLACK_PATHS)
     session.run("flake8", "google", "tests")
 
 
-@nox.session(python="3.6")
+@nox.session(python=DEFAULT_PYTHON_VERSION)
 def blacken(session):
     """Run black.
 
     Format code to uniform standard.
-
-    This currently uses Python 3.6 due to the automated Kokoro run of synthtool.
-    That run uses an image that doesn't have 3.6 installed. Before updating this
-    check the state of the `gcp_ubuntu_config` we use for that Kokoro run.
     """
-    session.install(BLACK_VERSION)
+    session.install(BLACK_VERSION, "click<8.1")
     session.run("black", *BLACK_PATHS)
 
 
-@nox.session(python="3.7")
+@nox.session(python=DEFAULT_PYTHON_VERSION)
 def lint_setup_py(session):
     """Verify that setup.py is valid (including RST check)."""
     session.install("docutils", "pygments")
@@ -120,7 +121,7 @@ def system(session):
         session.run("py.test", "--quiet", system_test_folder_path, *session.posargs)
 
 
-@nox.session(python="3.7")
+@nox.session(python=DEFAULT_PYTHON_VERSION)
 def cover(session):
     """Run the final coverage report.
 
@@ -133,12 +134,12 @@ def cover(session):
     session.run("coverage", "erase")
 
 
-@nox.session(python="3.7")
+@nox.session(python=DEFAULT_PYTHON_VERSION)
 def docs(session):
     """Build the docs for this library."""
 
     session.install("-e", ".")
-    session.install("sphinx<3.0.0", "alabaster", "recommonmark")
+    session.install("sphinx<3.0.0", "jinja2<3.1", "alabaster", "recommonmark")
 
     shutil.rmtree(os.path.join("docs", "_build"), ignore_errors=True)
     session.run(
diff --git a/setup.py b/setup.py
index 483a9cdb..a6c7153e 100644
--- a/setup.py
+++ b/setup.py
@@ -29,7 +29,8 @@
 # 'Development Status :: 5 - Production/Stable'
 release_status = "Development Status :: 4 - Beta"
 dependencies = [
-    "google-api-core[grpc] >= 1.31.5, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.0"
+    "google-api-core[grpc] >= 1.31.5, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.0",
+    "protobuf<4.0.0dev",
 ]
 extras = {}