diff --git a/example/Cargo.toml b/example/Cargo.toml
index c873be51..c889df5e 100644
--- a/example/Cargo.toml
+++ b/example/Cargo.toml
@@ -11,7 +11,7 @@ homepage = "https://github.com/alipay/ttrpc-rust"
 description = "An example of ttrpc."
 
 [dev-dependencies]
-protobuf = "2.8.0"
+protobuf = "2.27.1"
 bytes = "0.4.11"
 libc = "0.2.79"
 byteorder = "1.3.2"
diff --git a/example/protocols/protos/health.proto b/example/protocols/protos/health.proto
index effdbaae..0afb1b65 100644
--- a/example/protocols/protos/health.proto
+++ b/example/protocols/protos/health.proto
@@ -17,6 +17,7 @@ option (gogoproto.benchgen_all) = true;
 
 message CheckRequest {
 	string service = 1;
+	optional string option_val = 2;
 }
 
 message HealthCheckResponse {