diff --git a/src/shrpx_http2_upstream.cc b/src/shrpx_http2_upstream.cc
index bc0de69c..de1dec18 100644
--- a/src/shrpx_http2_upstream.cc
+++ b/src/shrpx_http2_upstream.cc
@@ -169,7 +169,8 @@ int on_header_callback(nghttp2_session *session, const nghttp2_frame *frame,
 
   if (downstream->get_request_headers_sum() + namelen + valuelen >
           get_config()->header_field_buffer ||
-      downstream->get_request_headers().size() >=
+      downstream->get_request_headers().size() +
+              downstream->get_request_trailers().size() >=
           get_config()->max_header_fields) {
     if (downstream->get_response_state() == Downstream::MSG_COMPLETE) {
       return 0;
diff --git a/src/shrpx_https_upstream.cc b/src/shrpx_https_upstream.cc
index 1acd8f4a..8f584749 100644
--- a/src/shrpx_https_upstream.cc
+++ b/src/shrpx_https_upstream.cc
@@ -146,7 +146,8 @@ int htp_hdr_keycb(http_parser *htp, const char *data, size_t len) {
     if (downstream->get_request_trailer_key_prev()) {
       downstream->append_last_request_trailer_key(data, len);
     } else {
-      if (downstream->get_request_headers().size() >=
+      if (downstream->get_request_headers().size() +
+              downstream->get_request_trailers().size() >=
           get_config()->max_header_fields) {
         if (LOG_ENABLED(INFO)) {
           ULOG(INFO, upstream) << "Too many header field num="
diff --git a/src/shrpx_spdy_upstream.cc b/src/shrpx_spdy_upstream.cc
index d7d2269a..604fb612 100644
--- a/src/shrpx_spdy_upstream.cc
+++ b/src/shrpx_spdy_upstream.cc
@@ -169,6 +169,8 @@ void on_ctrl_recv_callback(spdylay_session *session, spdylay_frame_type type,
       header_buffer += strlen(nv[i]) + strlen(nv[i + 1]);
     }
 
+    // spdy does not define usage of trailer fields, and we ignores
+    // them.
     if (header_buffer > get_config()->header_field_buffer ||
         num_headers > get_config()->max_header_fields) {
       upstream->rst_stream(downstream, SPDYLAY_INTERNAL_ERROR);