diff --git a/README.md b/README.md
index d4b4011..7519646 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,7 @@ cmake --build build
   - don't use it if you're unsure
 - `extra-listen-port` (since 0.3.0, [689f0e7](https://github.com/brevent/wss-proxy/commit/689f0e7)), extra listen port for shadowsocks client without sip003u
 - `syslog` (since 0.3.3, [47d4681](https://github.com/brevent/wss-proxy/commit/47d4681)), log to syslog if supported
+- `ipv6` (since 0.3.4, [a8b5f71](https://github.com/brevent/wss-proxy/commit/a8b5f71)), prefer ipv6 (should fallback to ipv4 if no ipv6)
 
 ### Server