diff --git a/src/tateyama/endpoint/stream/stream_response.cpp b/src/tateyama/endpoint/stream/stream_response.cpp
index aadc9d71..513f7d5e 100644
--- a/src/tateyama/endpoint/stream/stream_response.cpp
+++ b/src/tateyama/endpoint/stream/stream_response.cpp
@@ -29,7 +29,7 @@ namespace tateyama::common::stream {
 class stream_request;
 
 // class stream_response
-stream_response::stream_response(std::shared_ptr<tateyama::common::stream::stream_socket> stream, unsigned char index)
+stream_response::stream_response(std::shared_ptr<tateyama::common::stream::stream_socket> stream, std::uint16_t index)
     : session_socket_(std::move(stream)), index_(index) {
 }
 
diff --git a/src/tateyama/endpoint/stream/stream_response.h b/src/tateyama/endpoint/stream/stream_response.h
index ee9cb7a5..ca206845 100644
--- a/src/tateyama/endpoint/stream/stream_response.h
+++ b/src/tateyama/endpoint/stream/stream_response.h
@@ -79,7 +79,7 @@ class stream_response : public tateyama::api::server::response {
     friend stream_data_channel;
 
 public:
-    stream_response(std::shared_ptr<tateyama::common::stream::stream_socket> stream, unsigned char index);
+    stream_response(std::shared_ptr<tateyama::common::stream::stream_socket> stream, std::uint16_t index);
     stream_response() = delete;
 
     tateyama::status body(std::string_view body) override;
@@ -93,7 +93,7 @@ class stream_response : public tateyama::api::server::response {
     }
 private:
     std::shared_ptr<tateyama::common::stream::stream_socket> session_socket_;
-    unsigned char index_;
+    std::uint16_t index_;
 
     std::string message_{};