diff --git a/test/cpp/interop/xds_interop_client.cc b/test/cpp/interop/xds_interop_client.cc
index a229eb5588a..3b80ea4eab3 100644
--- a/test/cpp/interop/xds_interop_client.cc
+++ b/test/cpp/interop/xds_interop_client.cc
@@ -117,7 +117,7 @@ class XdsStatsWatcher {
 
 class TestClient {
  public:
-  TestClient(std::shared_ptr<Channel> channel)
+  TestClient(const std::shared_ptr<Channel>& channel)
       : stub_(TestService::NewStub(channel)) {}
 
   void UnaryCall() {
diff --git a/test/cpp/interop/xds_interop_server.cc b/test/cpp/interop/xds_interop_server.cc
index 0c7e594817b..59f2328cba8 100644
--- a/test/cpp/interop/xds_interop_server.cc
+++ b/test/cpp/interop/xds_interop_server.cc
@@ -52,7 +52,7 @@ using grpc::testing::TestService;
 
 class TestServiceImpl : public TestService::Service {
  public:
-  TestServiceImpl(std::string i) : hostname_(i) {}
+  TestServiceImpl(const std::string& i) : hostname_(i) {}
 
   Status UnaryCall(ServerContext* context, const SimpleRequest* request,
                    SimpleResponse* response) {
@@ -65,7 +65,7 @@ class TestServiceImpl : public TestService::Service {
   std::string hostname_;
 };
 
-void RunServer(const int port, std::string hostname) {
+void RunServer(const int port, const std::string& hostname) {
   std::ostringstream server_address;
   server_address << "0.0.0.0:" << port;