diff --git a/include/ylt/coro_rpc/impl/coro_connection.hpp b/include/ylt/coro_rpc/impl/coro_connection.hpp
index f01e739fb..a18be38c7 100644
--- a/include/ylt/coro_rpc/impl/coro_connection.hpp
+++ b/include/ylt/coro_rpc/impl/coro_connection.hpp
@@ -23,13 +23,10 @@
 #include <atomic>
 #include <cstdint>
 #include <functional>
-#include <future>
 #include <memory>
 #include <string_view>
 #include <system_error>
 #include <utility>
-#include <variant>
-#include <vector>
 #include <ylt/easylog.hpp>
 
 #include "ylt/coro_io/coro_io.hpp"
diff --git a/include/ylt/coro_rpc/impl/errno.h b/include/ylt/coro_rpc/impl/errno.h
index ccfa0c60a..6c2f2d573 100644
--- a/include/ylt/coro_rpc/impl/errno.h
+++ b/include/ylt/coro_rpc/impl/errno.h
@@ -16,7 +16,7 @@
 #include <ylt/struct_pack/util.h>
 #pragma once
 namespace coro_rpc {
-enum class errc : uint8_t {
+enum class errc : uint16_t {
   ok,
   io_error,
   not_connected,
@@ -29,8 +29,8 @@ enum class errc : uint8_t {
   protocol_error,
   message_too_large,
   server_has_ran,
-  user_defined_err_min = 100,
-  user_defined_err_max = 255
+  user_defined_err_min = 256,
+  user_defined_err_max = 65535
 };
 inline bool operator!(errc ec) { return ec == errc::ok; }
 inline std::string_view make_error_message(errc ec) {
diff --git a/include/ylt/coro_rpc/impl/protocol/coro_rpc_protocol.hpp b/include/ylt/coro_rpc/impl/protocol/coro_rpc_protocol.hpp
index 70f93e433..0e448baee 100644
--- a/include/ylt/coro_rpc/impl/protocol/coro_rpc_protocol.hpp
+++ b/include/ylt/coro_rpc/impl/protocol/coro_rpc_protocol.hpp
@@ -66,11 +66,11 @@ struct coro_rpc_protocol {
   struct resp_header {
     uint8_t magic;           //!< magic number
     uint8_t version;         //!< rpc protocol version
-    uint8_t err_code;        //!< rpc error type
-    uint8_t msg_type;        //!< message type
+    uint16_t err_code;       //!< rpc error type
     uint32_t seq_num;        //!< sequence number
     uint32_t length;         //!< length of RPC body
     uint32_t attach_length;  //!< reserved field
+    uint8_t msg_type;        //!< message type
   };
 
   using supported_serialize_protocols = std::variant<struct_pack_protocol>;
@@ -151,7 +151,7 @@ struct coro_rpc_protocol {
     auto& resp_head = *(resp_header*)header_buf.data();
     resp_head.magic = magic_number;
     resp_head.seq_num = req_header.seq_num;
-    resp_head.err_code = static_cast<uint8_t>(rpc_err_code);
+    resp_head.err_code = static_cast<uint16_t>(rpc_err_code);
     resp_head.attach_length = attachment_len;
     if (rpc_err_code != coro_rpc::errc{})
       AS_UNLIKELY {
@@ -179,7 +179,7 @@ struct coro_rpc_protocol {
   static_assert(REQ_HEAD_LEN == 20);
 
   static constexpr auto RESP_HEAD_LEN = sizeof(resp_header{});
-  static_assert(RESP_HEAD_LEN == 16);
+  static_assert(RESP_HEAD_LEN == 20);
 };
 }  // namespace protocol
 template <typename return_msg_type>