diff --git a/src/shrpx_http2_upstream.cc b/src/shrpx_http2_upstream.cc
index 2d7e2876..50e5a81e 100644
--- a/src/shrpx_http2_upstream.cc
+++ b/src/shrpx_http2_upstream.cc
@@ -372,6 +372,10 @@ int Http2Upstream::on_request_headers(Downstream *downstream,
 
   if (!(frame->hd.flags & NGHTTP2_FLAG_END_STREAM)) {
     req.http2_expect_body = true;
+  } else if (req.fs.content_length == -1) {
+    // If END_STREAM flag is set to HEADERS frame, we are sure that
+    // content-length is 0.
+    req.fs.content_length = 0;
   }
 
   downstream->inspect_http2_request();
@@ -643,6 +647,9 @@ int on_frame_send_callback(nghttp2_session *session, const nghttp2_frame *frame,
     req.http_major = 2;
     req.http_minor = 0;
 
+    req.fs.content_length = 0;
+    req.http2_expect_body = false;
+
     auto &promised_balloc = promised_downstream->get_block_allocator();
 
     for (size_t i = 0; i < frame->push_promise.nvlen; ++i) {
@@ -2072,6 +2079,9 @@ Http2Upstream::on_downstream_push_promise(Downstream *downstream,
   promised_req.http_major = 2;
   promised_req.http_minor = 0;
 
+  promised_req.fs.content_length = 0;
+  promised_req.http2_expect_body = false;
+
   auto ptr = promised_downstream.get();
   add_pending_downstream(std::move(promised_downstream));
   downstream_queue_.mark_active(ptr);
diff --git a/src/shrpx_http_downstream_connection.cc b/src/shrpx_http_downstream_connection.cc
index 9a454a21..b743526b 100644
--- a/src/shrpx_http_downstream_connection.cc
+++ b/src/shrpx_http_downstream_connection.cc
@@ -525,7 +525,13 @@ int HttpDownstreamConnection::push_request_headers() {
                       << downstream_->get_stream_id() << "\n" << nhdrs;
   }
 
-  signal_write();
+  // Don't call signal_write() if we anticipate request body.  We call
+  // signal_write() when we received request body chunk, and it
+  // enables us to send headers and data in one writev system call.
+  if (connect_method ||
+      (!req.http2_expect_body && req.fs.content_length == 0)) {
+    signal_write();
+  }
 
   return 0;
 }
diff --git a/src/shrpx_https_upstream.cc b/src/shrpx_https_upstream.cc
index 0be62b62..863f8d62 100644
--- a/src/shrpx_https_upstream.cc
+++ b/src/shrpx_https_upstream.cc
@@ -312,10 +312,19 @@ int htp_hdrs_completecb(http_parser *htp) {
     ULOG(INFO, upstream) << "HTTP request headers\n" << ss.str();
   }
 
-  // set content-length if no transfer-encoding is given.  If
-  // transfer-encoding is given, leave req.fs.content_length to -1.
-  if (!req.fs.header(http2::HD_TRANSFER_ENCODING)) {
-    req.fs.content_length = htp->content_length;
+  // set content-length if method is not CONNECT, and no
+  // transfer-encoding is given.  If transfer-encoding is given, leave
+  // req.fs.content_length to -1.
+  if (method != HTTP_CONNECT && !req.fs.header(http2::HD_TRANSFER_ENCODING)) {
+    // http-parser returns (uint64_t)-1 if there is no content-length
+    // header field.  If we don't have both transfer-encoding, and
+    // content-length header field, we assume that there is no request
+    // body.
+    if (htp->content_length == std::numeric_limits<uint64_t>::max()) {
+      req.fs.content_length = 0;
+    } else {
+      req.fs.content_length = htp->content_length;
+    }
   }
 
   auto host = req.fs.header(http2::HD_HOST);
diff --git a/src/shrpx_spdy_upstream.cc b/src/shrpx_spdy_upstream.cc
index 8077d426..fa0ffc94 100644
--- a/src/shrpx_spdy_upstream.cc
+++ b/src/shrpx_spdy_upstream.cc
@@ -305,6 +305,8 @@ void on_ctrl_recv_callback(spdylay_session *session, spdylay_frame_type type,
 
     if (!(frame->syn_stream.hd.flags & SPDYLAY_CTRL_FLAG_FIN)) {
       req.http2_expect_body = true;
+    } else if (req.fs.content_length == -1) {
+      req.fs.content_length = 0;
     }
 
     downstream->inspect_http2_request();