diff --git a/doc/admin-guide/files/records.config.en.rst b/doc/admin-guide/files/records.config.en.rst
index f5b11e4e180..106541a4f2f 100644
--- a/doc/admin-guide/files/records.config.en.rst
+++ b/doc/admin-guide/files/records.config.en.rst
@@ -3694,7 +3694,7 @@ HTTP/2 Configuration
    :ts:cv:`proxy.config.http2.min_concurrent_streams_in`.
    To disable, set to zero (``0``).
 
-.. ts:cv:: CONFIG proxy.config.http2.initial_window_size_in INT 1048576
+.. ts:cv:: CONFIG proxy.config.http2.initial_window_size_in INT 65535
    :reloadable:
 
    The initial window size for inbound connections.
@@ -3824,7 +3824,6 @@ HTTP/2 Configuration
    Clients that send smaller window increments lower than this limit will be immediately disconnected with an error
    code of ENHANCE_YOUR_CALM.
 
-
 HTTP/3 Configuration
 ====================
 
diff --git a/mgmt/RecordsConfig.cc b/mgmt/RecordsConfig.cc
index a7f7cb25dc7..99d7a6c15e1 100644
--- a/mgmt/RecordsConfig.cc
+++ b/mgmt/RecordsConfig.cc
@@ -1291,7 +1291,7 @@ static const RecordElement RecordsConfig[] =
   ,
   {RECT_CONFIG, "proxy.config.http2.max_active_streams_in", RECD_INT, "0", RECU_DYNAMIC, RR_NULL, RECC_STR, "^[0-9]+$", RECA_NULL}
   ,
-  {RECT_CONFIG, "proxy.config.http2.initial_window_size_in", RECD_INT, "1048576", RECU_DYNAMIC, RR_NULL, RECC_STR, "^[0-9]+$", RECA_NULL}
+  {RECT_CONFIG, "proxy.config.http2.initial_window_size_in", RECD_INT, "65535", RECU_DYNAMIC, RR_NULL, RECC_STR, "^[0-9]+$", RECA_NULL}
   ,
   {RECT_CONFIG, "proxy.config.http2.max_frame_size", RECD_INT, "16384", RECU_DYNAMIC, RR_NULL, RECC_STR, "^[0-9]+$", RECA_NULL}
   ,
diff --git a/proxy/http2/HTTP2.cc b/proxy/http2/HTTP2.cc
index ec5a5fb2330..fdaae905a1c 100644
--- a/proxy/http2/HTTP2.cc
+++ b/proxy/http2/HTTP2.cc
@@ -712,7 +712,7 @@ uint32_t Http2::min_concurrent_streams_in      = 10;
 uint32_t Http2::max_active_streams_in          = 0;
 bool Http2::throttling                         = false;
 uint32_t Http2::stream_priority_enabled        = 0;
-uint32_t Http2::initial_window_size            = 1048576;
+uint32_t Http2::initial_window_size            = 65535;
 uint32_t Http2::max_frame_size                 = 16384;
 uint32_t Http2::header_table_size              = 4096;
 uint32_t Http2::max_header_list_size           = 4294967295;
diff --git a/proxy/http2/Http2ClientSession.cc b/proxy/http2/Http2ClientSession.cc
index 18133bb1ad7..2ecfa2ece50 100644
--- a/proxy/http2/Http2ClientSession.cc
+++ b/proxy/http2/Http2ClientSession.cc
@@ -385,11 +385,9 @@ Http2ClientSession::main_event_handler(int event, void *edata)
     break;
 
   case VC_EVENT_WRITE_READY:
-    retval = 0;
-    break;
-
   case VC_EVENT_WRITE_COMPLETE:
-    // Seems as this is being closed already
+    this->connection_state.restart_streams();
+
     retval = 0;
     break;
 
@@ -678,6 +676,12 @@ Http2ClientSession::_should_do_something_else()
   return (this->_n_frame_read & 0x7F) == 0;
 }
 
+int64_t
+Http2ClientSession::write_avail()
+{
+  return this->write_buffer->write_avail();
+}
+
 NetVConnection *
 Http2ClientSession::get_netvc() const
 {
diff --git a/proxy/http2/Http2ClientSession.h b/proxy/http2/Http2ClientSession.h
index 12be63dea29..dfdb34ccb8e 100644
--- a/proxy/http2/Http2ClientSession.h
+++ b/proxy/http2/Http2ClientSession.h
@@ -134,6 +134,8 @@ class Http2ClientSession : public ProxySession
   // Record history from Http2ConnectionState
   void remember(const SourceLocation &location, int event, int reentrant = NO_REENTRANT);
 
+  int64_t write_avail();
+
   // noncopyable
   Http2ClientSession(Http2ClientSession &) = delete;
   Http2ClientSession &operator=(const Http2ClientSession &) = delete;
diff --git a/proxy/http2/Http2ConnectionState.cc b/proxy/http2/Http2ConnectionState.cc
index f8f57bffb8f..5386e5a9da4 100644
--- a/proxy/http2/Http2ConnectionState.cc
+++ b/proxy/http2/Http2ConnectionState.cc
@@ -166,6 +166,12 @@ rcv_data_frame(Http2ConnectionState &cstate, const Http2Frame &frame)
   cstate.decrement_server_rwnd(payload_length);
   stream->decrement_server_rwnd(payload_length);
 
+  if (is_debug_tag_set("http2_con")) {
+    uint32_t rwnd = cstate.server_settings.get(HTTP2_SETTINGS_INITIAL_WINDOW_SIZE);
+    Http2StreamDebug(cstate.ua_session, id, "Received DATA frame: rwnd con=%zd/%" PRId32 " stream=%zd/%" PRId32,
+                     cstate.server_rwnd(), rwnd, stream->server_rwnd(), rwnd);
+  }
+
   const uint32_t unpadded_length = payload_length - pad_length;
   MIOBuffer *writer              = stream->read_vio_writer();
   if (writer == nullptr) {
@@ -202,21 +208,6 @@ rcv_data_frame(Http2ConnectionState &cstate, const Http2Frame &frame)
     stream->signal_read_event(VC_EVENT_READ_READY);
   }
 
-  uint32_t initial_rwnd = cstate.server_settings.get(HTTP2_SETTINGS_INITIAL_WINDOW_SIZE);
-  uint32_t min_rwnd     = std::min(initial_rwnd, cstate.server_settings.get(HTTP2_SETTINGS_MAX_FRAME_SIZE));
-  // Connection level WINDOW UPDATE
-  if (cstate.server_rwnd() <= min_rwnd) {
-    Http2WindowSize diff_size = initial_rwnd - cstate.server_rwnd();
-    cstate.increment_server_rwnd(diff_size);
-    cstate.send_window_update_frame(0, diff_size);
-  }
-  // Stream level WINDOW UPDATE
-  if (stream->server_rwnd() <= min_rwnd) {
-    Http2WindowSize diff_size = initial_rwnd - stream->server_rwnd();
-    stream->increment_server_rwnd(diff_size);
-    cstate.send_window_update_frame(stream->get_id(), diff_size);
-  }
-
   return Http2Error(Http2ErrorClass::HTTP2_ERROR_CLASS_NONE);
 }
 
@@ -1288,6 +1279,35 @@ Http2ConnectionState::restart_streams()
   }
 }
 
+void
+Http2ConnectionState::restart_receiving(Http2Stream *stream)
+{
+  uint32_t initial_rwnd = this->server_settings.get(HTTP2_SETTINGS_INITIAL_WINDOW_SIZE);
+  uint32_t min_rwnd     = std::min(initial_rwnd, this->server_settings.get(HTTP2_SETTINGS_MAX_FRAME_SIZE));
+
+  // Connection level WINDOW UPDATE
+  if (this->server_rwnd() < min_rwnd) {
+    Http2WindowSize diff_size = initial_rwnd - this->server_rwnd();
+    this->increment_server_rwnd(diff_size);
+    this->send_window_update_frame(0, diff_size);
+  }
+
+  // Stream level WINDOW UPDATE
+  if (stream == nullptr || stream->server_rwnd() >= min_rwnd) {
+    return;
+  }
+
+  // If read_vio is buffering data, do not fully update window
+  int64_t data_size = stream->read_vio_read_avail();
+  if (data_size >= initial_rwnd) {
+    return;
+  }
+
+  Http2WindowSize diff_size = initial_rwnd - std::max(static_cast<int64_t>(stream->server_rwnd()), data_size);
+  stream->increment_server_rwnd(diff_size);
+  this->send_window_update_frame(stream->get_id(), diff_size);
+}
+
 void
 Http2ConnectionState::cleanup_streams()
 {
@@ -1497,6 +1517,11 @@ Http2ConnectionState::send_a_data_frame(Http2Stream *stream, size_t &payload_len
     return Http2SendDataFrameResult::ERROR;
   }
 
+  if (this->ua_session->write_avail() == 0) {
+    Http2StreamDebug(this->ua_session, stream->get_id(), "Not write avail");
+    return Http2SendDataFrameResult::NOT_WRITE_AVAIL;
+  }
+
   // Select appropriate payload length
   if (resp_reader->is_read_avail_more_than(0)) {
     // We only need to check for window size when there is a payload
@@ -1872,7 +1897,7 @@ Http2ConnectionState::send_goaway_frame(Http2StreamId id, Http2ErrorCode ec)
 void
 Http2ConnectionState::send_window_update_frame(Http2StreamId id, uint32_t size)
 {
-  Http2StreamDebug(ua_session, id, "Send WINDOW_UPDATE frame");
+  Http2StreamDebug(ua_session, id, "Send WINDOW_UPDATE frame: size=%" PRIu32, size);
 
   // Create WINDOW_UPDATE frame
   Http2WindowUpdateFrame window_update(id, size);
diff --git a/proxy/http2/Http2ConnectionState.h b/proxy/http2/Http2ConnectionState.h
index 6ba4ffea022..1c4986d6a45 100644
--- a/proxy/http2/Http2ConnectionState.h
+++ b/proxy/http2/Http2ConnectionState.h
@@ -39,6 +39,7 @@ enum class Http2SendDataFrameResult {
   NO_ERROR = 0,
   NO_WINDOW,
   NO_PAYLOAD,
+  NOT_WRITE_AVAIL,
   ERROR,
   DONE,
 };
@@ -134,6 +135,8 @@ class Http2ConnectionState : public Continuation
   void
   init()
   {
+    this->_server_rwnd = Http2::initial_window_size;
+
     local_hpack_handle  = new HpackHandle(HTTP2_HEADER_TABLE_SIZE);
     remote_hpack_handle = new HpackHandle(HTTP2_HEADER_TABLE_SIZE);
     if (Http2::stream_priority_enabled) {
@@ -190,7 +193,7 @@ class Http2ConnectionState : public Continuation
   bool delete_stream(Http2Stream *stream);
   void release_stream();
   void cleanup_streams();
-
+  void restart_receiving(Http2Stream *stream);
   void update_initial_rwnd(Http2WindowSize new_size);
 
   Http2StreamId
@@ -377,7 +380,7 @@ class Http2ConnectionState : public Continuation
 
   // Connection level window size
   ssize_t _client_rwnd = HTTP2_INITIAL_WINDOW_SIZE;
-  ssize_t _server_rwnd = Http2::initial_window_size;
+  ssize_t _server_rwnd = 0;
 
   std::vector<size_t> _recent_rwnd_increment = {SIZE_MAX, SIZE_MAX, SIZE_MAX, SIZE_MAX, SIZE_MAX};
   int _recent_rwnd_increment_index           = 0;
diff --git a/proxy/http2/Http2Stream.cc b/proxy/http2/Http2Stream.cc
index 7863cb2a8a7..4d4c1eed144 100644
--- a/proxy/http2/Http2Stream.cc
+++ b/proxy/http2/Http2Stream.cc
@@ -52,6 +52,7 @@ Http2Stream::init(Http2StreamId sid, ssize_t initial_rwnd)
   this->_id          = sid;
   this->_thread      = this_ethread();
   this->_client_rwnd = initial_rwnd;
+  this->_server_rwnd = Http2::initial_window_size;
 
   this->_reader = this->_request_buffer.alloc_reader();
   // FIXME: Are you sure? every "stream" needs request_header?
@@ -519,6 +520,19 @@ Http2Stream::update_read_request(int64_t read_len, bool call_update, bool check_
 void
 Http2Stream::restart_sending()
 {
+  if (!this->response_header_done) {
+    return;
+  }
+
+  IOBufferReader *reader = this->response_get_data_reader();
+  if (reader && !reader->is_read_avail_more_than(0)) {
+    return;
+  }
+
+  if (this->write_vio.mutex && this->write_vio.ntodo() == 0) {
+    return;
+  }
+
   this->send_response_body(true);
 }
 
@@ -719,6 +733,12 @@ Http2Stream::reenable(VIO *vio)
       SCOPED_MUTEX_LOCK(lock, this->mutex, this_ethread());
       update_write_request(vio->get_reader(), INT64_MAX, true);
     } else if (vio->op == VIO::READ) {
+      Http2ClientSession *h2_proxy_ssn = static_cast<Http2ClientSession *>(this->_proxy_ssn);
+      {
+        SCOPED_MUTEX_LOCK(ssn_lock, h2_proxy_ssn->connection_state.mutex, this_ethread());
+        h2_proxy_ssn->connection_state.restart_receiving(this);
+      }
+
       SCOPED_MUTEX_LOCK(lock, this->mutex, this_ethread());
       update_read_request(INT64_MAX, true);
     }
@@ -979,3 +999,14 @@ Http2Stream::get_transaction_priority_dependence() const
     return priority_node->parent ? priority_node->parent->id : 0;
   }
 }
+
+int64_t
+Http2Stream::read_vio_read_avail()
+{
+  MIOBuffer *writer = this->read_vio.get_writer();
+  if (writer) {
+    return writer->max_read_avail();
+  }
+
+  return 0;
+}
diff --git a/proxy/http2/Http2Stream.h b/proxy/http2/Http2Stream.h
index 675d0899fd5..72bc06036a6 100644
--- a/proxy/http2/Http2Stream.h
+++ b/proxy/http2/Http2Stream.h
@@ -128,6 +128,7 @@ class Http2Stream : public ProxyTransaction
   bool has_trailing_header() const;
   void set_request_headers(HTTPHdr &h2_headers);
   MIOBuffer *read_vio_writer() const;
+  int64_t read_vio_read_avail();
 
   //////////////////
   // Variables
@@ -204,8 +205,8 @@ class Http2Stream : public ProxyTransaction
   uint64_t data_length = 0;
   uint64_t bytes_sent  = 0;
 
-  ssize_t _client_rwnd;
-  ssize_t _server_rwnd = Http2::initial_window_size;
+  ssize_t _client_rwnd = 0;
+  ssize_t _server_rwnd = 0;
 
   std::vector<size_t> _recent_rwnd_increment = {SIZE_MAX, SIZE_MAX, SIZE_MAX, SIZE_MAX, SIZE_MAX};
   int _recent_rwnd_increment_index           = 0;