diff --git a/tools/run_tests/run_xds_tests.py b/tools/run_tests/run_xds_tests.py
index 20a274cd090..f107adeefae 100755
--- a/tools/run_tests/run_xds_tests.py
+++ b/tools/run_tests/run_xds_tests.py
@@ -114,7 +114,9 @@ argp.add_argument(
     '--xds_v3_support',
     default=False,
     action='store_true',
-    help='Support xDS v3 via GRPC_XDS_EXPERIMENTAL_V3_SUPPORT')
+    help='Support xDS v3 via GRPC_XDS_EXPERIMENTAL_V3_SUPPORT. '
+    'If a pre-created bootstrap file is provided via the --bootstrap_file '
+    'parameter, it should include xds_v3 in its server_features field.')
 argp.add_argument(
     '--client_cmd',
     default=None,