diff --git a/noxfile.py b/noxfile.py
index db108f7..729c61e 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -164,7 +164,7 @@ def docs(session):
     """Build the docs for this library."""
 
     session.install("-e", ".")
-    session.install("sphinx", "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 72da45c..6ef1645 100644
--- a/setup.py
+++ b/setup.py
@@ -41,7 +41,8 @@
     include_package_data=True,
     install_requires=(
         "google-api-core[grpc] >= 1.31.5, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.0",
-        "proto-plus >= 1.4.0",
+        "proto-plus >= 1.4.0, <2.0.0dev",
+        "protobuf<4.0.0dev",
     ),
     python_requires=">=3.6",
     setup_requires=["libcst >= 0.2.5"],