diff --git a/noxfile.py b/noxfile.py
index e91dc8e2..479f81a1 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -18,6 +18,7 @@
 
 from __future__ import absolute_import
 import os
+import pathlib
 import shutil
 
 import nox
@@ -30,6 +31,8 @@
 SYSTEM_TEST_PYTHON_VERSIONS = ["3.8"]
 UNIT_TEST_PYTHON_VERSIONS = ["3.6", "3.7", "3.8", "3.9"]
 
+CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+
 # 'docfx' is excluded since it only needs to run in 'docs-presubmit'
 nox.options.sessions = [
     "unit",
@@ -84,13 +87,15 @@ def lint_setup_py(session):
 
 def default(session):
     # Install all test dependencies, then install this package in-place.
-    session.install("asyncmock", "pytest-asyncio")
 
-    session.install(
-        "mock", "pytest", "pytest-cov",
+    constraints_path = str(
+        CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
     )
+    session.install("asyncmock", "pytest-asyncio", "-c", constraints_path)
 
-    session.install("-e", ".")
+    session.install("mock", "pytest", "pytest-cov", "-c", constraints_path)
+
+    session.install("-e", ".", "-c", constraints_path)
 
     # Run py.test against the unit tests.
     session.run(
@@ -117,6 +122,9 @@ def unit(session):
 @nox.session(python=SYSTEM_TEST_PYTHON_VERSIONS)
 def system(session):
     """Run the system test suite."""
+    constraints_path = str(
+        CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
+    )
     system_test_path = os.path.join("tests", "system.py")
     system_test_folder_path = os.path.join("tests", "system")
 
@@ -141,10 +149,8 @@ def system(session):
 
     # Install all test dependencies, then install this package into the
     # virtualenv's dist-packages.
-    session.install(
-        "mock", "pytest", "google-cloud-testutils",
-    )
-    session.install("-e", ".")
+    session.install("mock", "pytest", "google-cloud-testutils", "-c", constraints_path)
+    session.install("-e", ".", "-c", constraints_path)
 
     # Run py.test against the system tests.
     if system_test_exists:
diff --git a/synth.metadata b/synth.metadata
index 33c77dbe..b986eb0f 100644
--- a/synth.metadata
+++ b/synth.metadata
@@ -19,14 +19,14 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "f5c5904fb0c6aa3b3730eadf4e5a4485afc65726"
+        "sha": "86ed43d4f56e6404d068e62e497029018879c771"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "f5c5904fb0c6aa3b3730eadf4e5a4485afc65726"
+        "sha": "86ed43d4f56e6404d068e62e497029018879c771"
       }
     }
   ],