diff --git a/setup.py b/setup.py
index 5944afa..8bbc2aa 100644
--- a/setup.py
+++ b/setup.py
@@ -40,6 +40,7 @@
 dependencies = [
     "google-api-core[grpc] >= 1.34.0, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.*,!=2.4.*,!=2.5.*,!=2.6.*,!=2.7.*,!=2.8.*,!=2.9.*,!=2.10.*",
     "proto-plus >= 1.22.0, <2.0.0dev",
+    "proto-plus >= 1.22.2, <2.0.0dev; python_version>='3.11'",
     "protobuf>=3.19.5,<5.0.0dev,!=3.20.0,!=3.20.1,!=4.21.0,!=4.21.1,!=4.21.2,!=4.21.3,!=4.21.4,!=4.21.5",
 ]
 url = "https://github.com/googleapis/python-source-context"
@@ -79,6 +80,7 @@
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
+        "Programming Language :: Python :: 3.11",
         "Operating System :: OS Independent",
         "Topic :: Internet",
     ],
diff --git a/testing/constraints-3.12.txt b/testing/constraints-3.12.txt
new file mode 100644
index 0000000..ed7f9ae
--- /dev/null
+++ b/testing/constraints-3.12.txt
@@ -0,0 +1,6 @@
+# -*- coding: utf-8 -*-
+# This constraints file is required for unit tests.
+# List all library dependencies and extras in this file.
+google-api-core
+proto-plus
+protobuf