diff --git a/src/shrpx_http2_upstream.cc b/src/shrpx_http2_upstream.cc
index 7d48f563..c27fada3 100644
--- a/src/shrpx_http2_upstream.cc
+++ b/src/shrpx_http2_upstream.cc
@@ -1378,7 +1378,11 @@ int Http2Upstream::downstream_error(DownstreamConnection *dconn, int events) {
     } else {
       unsigned int status;
       if (events & Downstream::EVENT_TIMEOUT) {
-        status = 504;
+        if (downstream->get_request_header_sent()) {
+          status = 504;
+        } else {
+          status = 408;
+        }
       } else {
         status = 502;
       }
diff --git a/src/shrpx_https_upstream.cc b/src/shrpx_https_upstream.cc
index 3a543acd..bfe4f7c2 100644
--- a/src/shrpx_https_upstream.cc
+++ b/src/shrpx_https_upstream.cc
@@ -893,7 +893,11 @@ int HttpsUpstream::downstream_error(DownstreamConnection *dconn, int events) {
 
   unsigned int status;
   if (events & Downstream::EVENT_TIMEOUT) {
-    status = 504;
+    if (downstream->get_request_header_sent()) {
+      status = 504;
+    } else {
+      status = 408;
+    }
   } else {
     status = 502;
   }