diff --git a/src/shrpx_client_handler.cc b/src/shrpx_client_handler.cc
index ea8cea16..472db835 100644
--- a/src/shrpx_client_handler.cc
+++ b/src/shrpx_client_handler.cc
@@ -938,7 +938,8 @@ uint32_t ClientHandler::get_affinity_cookie(Downstream *downstream,
 }
 
 std::unique_ptr<DownstreamConnection>
-ClientHandler::get_downstream_connection(int &err, Downstream *downstream) {
+ClientHandler::get_downstream_connection(int &err, Downstream *downstream,
+                                         shrpx_proto pref_proto) {
   size_t group_idx;
   auto &downstreamconf = *worker_->get_downstream_config();
   auto &routerconf = downstreamconf.router;
@@ -1041,7 +1042,8 @@ ClientHandler::get_downstream_connection(int &err, Downstream *downstream) {
           i = 0;
         }
         addr = &shared_addr->addrs[shared_addr->affinity_hash[i].idx];
-        if (addr->connect_blocker->blocked()) {
+        if (addr->connect_blocker->blocked() ||
+            (pref_proto != PROTO_NONE && pref_proto != addr->proto)) {
           continue;
         }
         break;
@@ -1081,7 +1083,15 @@ ClientHandler::get_downstream_connection(int &err, Downstream *downstream) {
 
   auto proto = PROTO_NONE;
 
-  if (http1_weight > 0 && http2_weight > 0) {
+  if (pref_proto == PROTO_HTTP1) {
+    if (http1_weight > 0) {
+      proto = PROTO_HTTP1;
+    }
+  } else if (pref_proto == PROTO_HTTP2) {
+    if (http2_weight > 0) {
+      proto = PROTO_HTTP2;
+    }
+  } else if (http1_weight > 0 && http2_weight > 0) {
     // We only advance cycle if both weight has nonzero to keep its
     // distance under WEIGHT_MAX.
     if (pri_less(shared_addr->http1_pri, shared_addr->http2_pri)) {
diff --git a/src/shrpx_client_handler.h b/src/shrpx_client_handler.h
index 8d4073b7..9e1153bd 100644
--- a/src/shrpx_client_handler.h
+++ b/src/shrpx_client_handler.h
@@ -102,9 +102,11 @@ public:
   // Returns DownstreamConnection object based on request path.  This
   // function returns non-null DownstreamConnection, and assigns 0 to
   // |err| if it succeeds, or returns nullptr, and assigns negative
-  // error code to |err|.
+  // error code to |err|.  If |pref_proto| is not PROTO_NONE, choose
+  // backend whose protocol is |pref_proto|.
   std::unique_ptr<DownstreamConnection>
-  get_downstream_connection(int &err, Downstream *downstream);
+  get_downstream_connection(int &err, Downstream *downstream,
+                            shrpx_proto pref_proto = PROTO_NONE);
   MemchunkPool *get_mcpool();
   SSL *get_ssl() const;
   // Call this function when HTTP/2 connection header is received at
diff --git a/src/shrpx_http_downstream_connection.cc b/src/shrpx_http_downstream_connection.cc
index 0bcc41ad..29f01791 100644
--- a/src/shrpx_http_downstream_connection.cc
+++ b/src/shrpx_http_downstream_connection.cc
@@ -87,7 +87,11 @@ void retry_downstream_connection(Downstream *downstream,
   downstream->pop_downstream_connection();
 
   int rv;
-  auto ndconn = handler->get_downstream_connection(rv, downstream);
+  // We have to use h1 backend for retry if we have already written h1
+  // request in request buffer.
+  auto ndconn = handler->get_downstream_connection(
+      rv, downstream,
+      downstream->get_request_header_sent() ? PROTO_HTTP1 : PROTO_NONE);
   if (ndconn) {
     if (downstream->attach_downstream_connection(std::move(ndconn)) == 0 &&
         downstream->push_request_headers() == 0) {