diff --git a/src/shrpx_downstream.cc b/src/shrpx_downstream.cc
index dc7762d0..d3d40e51 100644
--- a/src/shrpx_downstream.cc
+++ b/src/shrpx_downstream.cc
@@ -113,7 +113,7 @@ void downstream_wtimeoutcb(struct ev_loop *loop, ev_timer *w, int revents) {
 
 // upstream could be nullptr for unittests
 Downstream::Downstream(Upstream *upstream, MemchunkPool *mcpool,
-                       int32_t stream_id)
+                       int64_t stream_id)
     : dlnext(nullptr),
       dlprev(nullptr),
       response_sent_body_length(0),
@@ -605,9 +605,9 @@ void Downstream::reset_upstream(Upstream *upstream) {
 
 Upstream *Downstream::get_upstream() const { return upstream_; }
 
-void Downstream::set_stream_id(int32_t stream_id) { stream_id_ = stream_id; }
+void Downstream::set_stream_id(int64_t stream_id) { stream_id_ = stream_id; }
 
-int32_t Downstream::get_stream_id() const { return stream_id_; }
+int64_t Downstream::get_stream_id() const { return stream_id_; }
 
 void Downstream::set_request_state(DownstreamState state) {
   request_state_ = state;
@@ -904,11 +904,11 @@ StringRef Downstream::get_http2_settings() const {
   return http2_settings->value;
 }
 
-void Downstream::set_downstream_stream_id(int32_t stream_id) {
+void Downstream::set_downstream_stream_id(int64_t stream_id) {
   downstream_stream_id_ = stream_id;
 }
 
-int32_t Downstream::get_downstream_stream_id() const {
+int64_t Downstream::get_downstream_stream_id() const {
   return downstream_stream_id_;
 }
 
@@ -1115,11 +1115,11 @@ DefaultMemchunks Downstream::pop_response_buf() {
   return std::move(response_buf_);
 }
 
-void Downstream::set_assoc_stream_id(int32_t stream_id) {
+void Downstream::set_assoc_stream_id(int64_t stream_id) {
   assoc_stream_id_ = stream_id;
 }
 
-int32_t Downstream::get_assoc_stream_id() const { return assoc_stream_id_; }
+int64_t Downstream::get_assoc_stream_id() const { return assoc_stream_id_; }
 
 BlockAllocator &Downstream::get_block_allocator() { return balloc_; }
 
diff --git a/src/shrpx_downstream.h b/src/shrpx_downstream.h
index fff49a1a..10063b50 100644
--- a/src/shrpx_downstream.h
+++ b/src/shrpx_downstream.h
@@ -319,20 +319,20 @@ enum class DispatchState {
 
 class Downstream {
 public:
-  Downstream(Upstream *upstream, MemchunkPool *mcpool, int32_t stream_id);
+  Downstream(Upstream *upstream, MemchunkPool *mcpool, int64_t stream_id);
   ~Downstream();
   void reset_upstream(Upstream *upstream);
   Upstream *get_upstream() const;
-  void set_stream_id(int32_t stream_id);
-  int32_t get_stream_id() const;
-  void set_assoc_stream_id(int32_t stream_id);
-  int32_t get_assoc_stream_id() const;
+  void set_stream_id(int64_t stream_id);
+  int64_t get_stream_id() const;
+  void set_assoc_stream_id(int64_t stream_id);
+  int64_t get_assoc_stream_id() const;
   void pause_read(IOCtrlReason reason);
   int resume_read(IOCtrlReason reason, size_t consumed);
   void force_resume_read();
   // Set stream ID for downstream HTTP2 connection.
-  void set_downstream_stream_id(int32_t stream_id);
-  int32_t get_downstream_stream_id() const;
+  void set_downstream_stream_id(int64_t stream_id);
+  int64_t get_downstream_stream_id() const;
 
   int attach_downstream_connection(std::unique_ptr<DownstreamConnection> dconn);
   void detach_downstream_connection();
@@ -566,12 +566,12 @@ private:
   // How many times we tried in backend connection
   size_t num_retry_;
   // The stream ID in frontend connection
-  int32_t stream_id_;
+  int64_t stream_id_;
   // The associated stream ID in frontend connection if this is pushed
   // stream.
-  int32_t assoc_stream_id_;
+  int64_t assoc_stream_id_;
   // stream ID in backend connection
-  int32_t downstream_stream_id_;
+  int64_t downstream_stream_id_;
   // RST_STREAM error_code from downstream HTTP2 connection
   uint32_t response_rst_stream_error_code_;
   // An affinity cookie value.