diff --git a/doc/xds-test-descriptions.md b/doc/xds-test-descriptions.md
index 721b1e7414c..bea4a677aa5 100644
--- a/doc/xds-test-descriptions.md
+++ b/doc/xds-test-descriptions.md
@@ -39,6 +39,8 @@ Clients should accept these arguments:
 *   --stats_port=PORT
     *   The port for to expose the client's `LoadBalancerStatsService`
         implementation.
+*   --rpc_timeout_sec=SEC
+    *   The timeout to set on all outbound RPCs. Default is 20.
 
 ## Test Driver