diff --git a/.kokoro/build.sh b/.kokoro/build.sh
index 6c21d00..b96af36 100755
--- a/.kokoro/build.sh
+++ b/.kokoro/build.sh
@@ -36,4 +36,10 @@ python3.6 -m pip uninstall --yes --quiet nox-automation
 python3.6 -m pip install --upgrade --quiet nox
 python3.6 -m nox --version
 
-python3.6 -m nox
+# If NOX_SESSION is set, it only runs the specified session,
+# otherwise run all the sessions.
+if [[ -n "${NOX_SESSION:-}" ]]; then
+    python3.6 -m nox -s "${NOX_SESSION:-}"
+else
+    python3.6 -m nox
+fi
diff --git a/noxfile.py b/noxfile.py
index 6ab8c6e..5009268 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -100,6 +100,10 @@ def system(session):
     """Run the system test suite."""
     system_test_path = os.path.join("tests", "system.py")
     system_test_folder_path = os.path.join("tests", "system")
+
+    # Check the value of `RUN_SYSTEM_TESTS` env var. It defaults to true.
+    if os.environ.get("RUN_SYSTEM_TESTS", "true") == "false":
+        session.skip("RUN_SYSTEM_TESTS is set to false, skipping")
     # Sanity check: Only run tests if the environment variable is set.
     if not os.environ.get("GOOGLE_APPLICATION_CREDENTIALS", ""):
         session.skip("Credentials must be set via environment variable")
diff --git a/synth.metadata b/synth.metadata
index 060238d..74f107e 100644
--- a/synth.metadata
+++ b/synth.metadata
@@ -19,14 +19,14 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "39b527a39f5cd56d4882b3874fc08eed4756cebe"
+        "sha": "bfcdbe0da977b2de6c1c0471bb6dc2f1e13bf669"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "39b527a39f5cd56d4882b3874fc08eed4756cebe"
+        "sha": "bfcdbe0da977b2de6c1c0471bb6dc2f1e13bf669"
       }
     }
   ],