diff --git a/include/asio_net/detail/message.hpp b/include/asio_net/detail/message.hpp
index c2c1c64..f71d410 100644
--- a/include/asio_net/detail/message.hpp
+++ b/include/asio_net/detail/message.hpp
@@ -10,7 +10,7 @@ namespace detail {
 
 struct message : private noncopyable {
   message() = default;
-  explicit message(std::string msg) : length(msg.length()), body(std::move(msg)) {}
+  explicit message(std::string msg) : length((uint32_t)msg.length()), body(std::move(msg)) {}
 
   void clear() {
     length = 0;
diff --git a/include/asio_net/detail/tcp_channel_t.hpp b/include/asio_net/detail/tcp_channel_t.hpp
index 33fc48d..0ac3eb5 100644
--- a/include/asio_net/detail/tcp_channel_t.hpp
+++ b/include/asio_net/detail/tcp_channel_t.hpp
@@ -234,7 +234,7 @@ class tcp_channel_t : private noncopyable {
   typename socket_impl<T>::socket& socket_;
   const tcp_config& config_;
   detail::message read_msg_;
-  uint32_t send_buffer_now_ = 0;
+  size_t send_buffer_now_ = 0;
   std::deque<std::string> write_msg_queue_;
 };
 
diff --git a/include/asio_net/rpc_core b/include/asio_net/rpc_core
index 813ed97..992c1d0 160000
--- a/include/asio_net/rpc_core
+++ b/include/asio_net/rpc_core
@@ -1 +1 @@
-Subproject commit 813ed97c6cec4b349a25b280edbd4fa6413af4dd
+Subproject commit 992c1d059332cc0b63ddc964f43c8ca7d9f266b2
diff --git a/include/asio_net/serial_port.hpp b/include/asio_net/serial_port.hpp
index 0655fa8..8867dd9 100644
--- a/include/asio_net/serial_port.hpp
+++ b/include/asio_net/serial_port.hpp
@@ -96,18 +96,18 @@ class serial_port : detail::noncopyable {
     // queue for asio::async_write
     if (!from_queue && send_buffer_now_ != 0) {
       ASIO_NET_LOGV("queue for asio::async_write");
-      send_buffer_now_ += msg.size();
+      send_buffer_now_ += (uint32_t)msg.size();
       write_msg_queue_.emplace_back(std::move(msg));
       return;
     }
     if (!from_queue) {
-      send_buffer_now_ += msg.size();
+      send_buffer_now_ += (uint32_t)msg.size();
     }
 
     auto keeper = std::make_unique<detail::message>(std::move(msg));
     auto buffer = asio::buffer(keeper->body);
     asio::async_write(serial_, buffer, [this, keeper = std::move(keeper)](const std::error_code& ec, std::size_t /*length*/) {
-      send_buffer_now_ -= keeper->body.size();
+      send_buffer_now_ -= (uint32_t)keeper->body.size();
       if (ec) {
         do_close();
       }
diff --git a/test/udp_c.cpp b/test/udp_c.cpp
index 2780938..27ebfd0 100644
--- a/test/udp_c.cpp
+++ b/test/udp_c.cpp
@@ -10,7 +10,7 @@ int main() {
   udp_client client(context);
   udp_client::endpoint endpoint(asio::ip::address_v4::from_string("127.0.0.1"), PORT);
   client.send_to("hello", endpoint, [&](const std::error_code& ec, std::size_t size) {
-    LOG("result: ec: %d, size: %lu", ec.value(), size);
+    LOG("result: ec: %d, size: %zu", ec.value(), size);
   });
   context.run();
   return EXIT_SUCCESS;