diff --git a/src/http2.cc b/src/http2.cc
index 8385cafe..445ebe44 100644
--- a/src/http2.cc
+++ b/src/http2.cc
@@ -134,107 +134,107 @@ std::string get_status_string(unsigned int status_code) {
   }
 }
 
-const char *stringify_status(unsigned int status_code) {
+StringRef stringify_status(unsigned int status_code) {
   switch (status_code) {
   case 100:
-    return "100";
+    return StringRef::from_lit("100");
   case 101:
-    return "101";
+    return StringRef::from_lit("101");
   case 200:
-    return "200";
+    return StringRef::from_lit("200");
   case 201:
-    return "201";
+    return StringRef::from_lit("201");
   case 202:
-    return "202";
+    return StringRef::from_lit("202");
   case 203:
-    return "203";
+    return StringRef::from_lit("203");
   case 204:
-    return "204";
+    return StringRef::from_lit("204");
   case 205:
-    return "205";
+    return StringRef::from_lit("205");
   case 206:
-    return "206";
+    return StringRef::from_lit("206");
   case 300:
-    return "300";
+    return StringRef::from_lit("300");
   case 301:
-    return "301";
+    return StringRef::from_lit("301");
   case 302:
-    return "302";
+    return StringRef::from_lit("302");
   case 303:
-    return "303";
+    return StringRef::from_lit("303");
   case 304:
-    return "304";
+    return StringRef::from_lit("304");
   case 305:
-    return "305";
-  // case 306: return "306";
+    return StringRef::from_lit("305");
+  // case 306: return StringRef::from_lit("306");
   case 307:
-    return "307";
+    return StringRef::from_lit("307");
   case 308:
-    return "308";
+    return StringRef::from_lit("308");
   case 400:
-    return "400";
+    return StringRef::from_lit("400");
   case 401:
-    return "401";
+    return StringRef::from_lit("401");
   case 402:
-    return "402";
+    return StringRef::from_lit("402");
   case 403:
-    return "403";
+    return StringRef::from_lit("403");
   case 404:
-    return "404";
+    return StringRef::from_lit("404");
   case 405:
-    return "405";
+    return StringRef::from_lit("405");
   case 406:
-    return "406";
+    return StringRef::from_lit("406");
   case 407:
-    return "407";
+    return StringRef::from_lit("407");
   case 408:
-    return "408";
+    return StringRef::from_lit("408");
   case 409:
-    return "409";
+    return StringRef::from_lit("409");
   case 410:
-    return "410";
+    return StringRef::from_lit("410");
   case 411:
-    return "411";
+    return StringRef::from_lit("411");
   case 412:
-    return "412";
+    return StringRef::from_lit("412");
   case 413:
-    return "413";
+    return StringRef::from_lit("413");
   case 414:
-    return "414";
+    return StringRef::from_lit("414");
   case 415:
-    return "415";
+    return StringRef::from_lit("415");
   case 416:
-    return "416";
+    return StringRef::from_lit("416");
   case 417:
-    return "417";
+    return StringRef::from_lit("417");
   case 421:
-    return "421";
+    return StringRef::from_lit("421");
   case 426:
-    return "426";
+    return StringRef::from_lit("426");
   case 428:
-    return "428";
+    return StringRef::from_lit("428");
   case 429:
-    return "429";
+    return StringRef::from_lit("429");
   case 431:
-    return "431";
+    return StringRef::from_lit("431");
   case 451:
-    return "451";
+    return StringRef::from_lit("451");
   case 500:
-    return "500";
+    return StringRef::from_lit("500");
   case 501:
-    return "501";
+    return StringRef::from_lit("501");
   case 502:
-    return "502";
+    return StringRef::from_lit("502");
   case 503:
-    return "503";
+    return StringRef::from_lit("503");
   case 504:
-    return "504";
+    return StringRef::from_lit("504");
   case 505:
-    return "505";
+    return StringRef::from_lit("505");
   case 511:
-    return "511";
+    return StringRef::from_lit("511");
   default:
-    return nullptr;
+    return StringRef{};
   }
 }
 
diff --git a/src/http2.h b/src/http2.h
index 48d4916d..0ae9d3b3 100644
--- a/src/http2.h
+++ b/src/http2.h
@@ -98,7 +98,7 @@ std::string get_status_string(unsigned int status_code);
 
 // Returns string version of |status_code|.  This function can handle
 // only predefined status code.  Otherwise, returns nullptr.
-const char *stringify_status(unsigned int status_code);
+StringRef stringify_status(unsigned int status_code);
 
 void capitalize(DefaultMemchunks *buf, const StringRef &s);
 
diff --git a/src/shrpx-unittest.cc b/src/shrpx-unittest.cc
index 0f2e2fd2..725838f8 100644
--- a/src/shrpx-unittest.cc
+++ b/src/shrpx-unittest.cc
@@ -143,6 +143,8 @@ int main(int argc, char *argv[]) {
       !CU_add_test(pSuite, "util_ipv6_numeric_addr",
                    shrpx::test_util_ipv6_numeric_addr) ||
       !CU_add_test(pSuite, "util_utos", shrpx::test_util_utos) ||
+      !CU_add_test(pSuite, "util_make_string_ref_uint",
+                   shrpx::test_util_make_string_ref_uint) ||
       !CU_add_test(pSuite, "util_utos_unit", shrpx::test_util_utos_unit) ||
       !CU_add_test(pSuite, "util_utos_funit", shrpx::test_util_utos_funit) ||
       !CU_add_test(pSuite, "util_parse_uint_with_unit",
diff --git a/src/shrpx_http2_upstream.cc b/src/shrpx_http2_upstream.cc
index 79fac5de..e54b8e90 100644
--- a/src/shrpx_http2_upstream.cc
+++ b/src/shrpx_http2_upstream.cc
@@ -1229,20 +1229,20 @@ int Http2Upstream::send_reply(Downstream *downstream, const uint8_t *body,
   const auto &resp = downstream->response();
   auto &httpconf = get_config()->http;
 
+  auto &balloc = downstream->get_block_allocator();
+
   const auto &headers = resp.fs.headers();
   auto nva = std::vector<nghttp2_nv>();
   // 2 for :status and server
   nva.reserve(2 + headers.size() + httpconf.add_response_headers.size());
 
-  std::string status_code_str;
-  auto response_status_const = http2::stringify_status(resp.http_status);
-  if (response_status_const) {
-    nva.push_back(http2::make_nv_lc_nocopy(":status", response_status_const));
-  } else {
-    status_code_str = util::utos(resp.http_status);
-    nva.push_back(http2::make_nv_ls(":status", status_code_str));
+  auto response_status = http2::stringify_status(resp.http_status);
+  if (response_status.empty()) {
+    response_status = util::make_string_ref_uint(balloc, resp.http_status);
   }
 
+  nva.push_back(http2::make_nv_ls_nocopy(":status", response_status));
+
   for (auto &kv : headers) {
     if (kv.name.empty() || kv.name[0] == ':') {
       continue;
@@ -1290,6 +1290,8 @@ int Http2Upstream::error_reply(Downstream *downstream,
   int rv;
   auto &resp = downstream->response();
 
+  auto &balloc = downstream->get_block_allocator();
+
   auto html = http::create_error_html(status_code);
   resp.http_status = status_code;
   auto body = downstream->get_response_buf();
@@ -1303,20 +1305,20 @@ int Http2Upstream::error_reply(Downstream *downstream,
   auto lgconf = log_config();
   lgconf->update_tstamp(std::chrono::system_clock::now());
 
-  auto response_status_const = http2::stringify_status(status_code);
-  auto content_length = util::utos(html.size());
+  auto response_status = http2::stringify_status(status_code);
+  if (response_status.empty()) {
+    response_status = util::make_string_ref_uint(balloc, status_code);
+  }
 
-  std::string status_code_str;
+  auto content_length = util::make_string_ref_uint(balloc, html.size());
+  auto date = make_string_ref(balloc, StringRef{lgconf->time_http_str});
 
-  auto nva = make_array(
-      response_status_const
-          ? http2::make_nv_lc_nocopy(":status", response_status_const)
-          : http2::make_nv_ls(":status",
-                              (status_code_str = util::utos(status_code))),
-      http2::make_nv_ll("content-type", "text/html; charset=UTF-8"),
-      http2::make_nv_ls_nocopy("server", get_config()->http.server_name),
-      http2::make_nv_ls("content-length", content_length),
-      http2::make_nv_ls("date", lgconf->time_http_str));
+  auto nva = std::array<nghttp2_nv, 5>{
+      {http2::make_nv_ls_nocopy(":status", response_status),
+       http2::make_nv_ll("content-type", "text/html; charset=UTF-8"),
+       http2::make_nv_ls_nocopy("server", get_config()->http.server_name),
+       http2::make_nv_ls_nocopy("content-length", content_length),
+       http2::make_nv_ls_nocopy("date", date)}};
 
   rv = nghttp2_submit_response(session_, downstream->get_stream_id(),
                                nva.data(), nva.size(), &data_prd);
@@ -1357,6 +1359,8 @@ int Http2Upstream::on_downstream_header_complete(Downstream *downstream) {
   const auto &req = downstream->request();
   auto &resp = downstream->response();
 
+  auto &balloc = downstream->get_block_allocator();
+
   if (LOG_ENABLED(INFO)) {
     if (downstream->get_non_final_response()) {
       DLOG(INFO, downstream) << "HTTP non-final response header";
@@ -1396,16 +1400,14 @@ int Http2Upstream::on_downstream_header_complete(Downstream *downstream) {
   nva.reserve(resp.fs.headers().size() + 4 +
               httpconf.add_response_headers.size());
   std::string via_value;
-  std::string response_status;
 
-  auto response_status_const = http2::stringify_status(resp.http_status);
-  if (response_status_const) {
-    nva.push_back(http2::make_nv_lc_nocopy(":status", response_status_const));
-  } else {
-    response_status = util::utos(resp.http_status);
-    nva.push_back(http2::make_nv_ls(":status", response_status));
+  auto response_status = http2::stringify_status(resp.http_status);
+  if (response_status.empty()) {
+    response_status = util::make_string_ref_uint(balloc, resp.http_status);
   }
 
+  nva.push_back(http2::make_nv_ls_nocopy(":status", response_status));
+
   if (downstream->get_non_final_response()) {
     http2::copy_headers_to_nva(nva, resp.fs.headers());
 
diff --git a/src/shrpx_mruby_module_response.cc b/src/shrpx_mruby_module_response.cc
index 65fec390..8a89a058 100644
--- a/src/shrpx_mruby_module_response.cc
+++ b/src/shrpx_mruby_module_response.cc
@@ -215,14 +215,7 @@ mrb_value response_return(mrb_state *mrb, mrb_value self) {
     bodylen = vallen;
   }
 
-  StringRef content_length;
-  {
-    auto iov = make_byte_ref(balloc, str_size("18446744073709551615") + 1);
-    auto p = iov.base;
-    p = util::utos(p, bodylen);
-    *p = '\0';
-    content_length = StringRef{iov.base, p};
-  }
+  auto content_length = util::make_string_ref_uint(balloc, bodylen);
 
   auto cl = resp.fs.header(http2::HD_CONTENT_LENGTH);
   if (cl) {
diff --git a/src/util.h b/src/util.h
index 4f926e2a..2d3208fc 100644
--- a/src/util.h
+++ b/src/util.h
@@ -51,6 +51,7 @@
 
 #include "template.h"
 #include "network.h"
+#include "allocator.h"
 
 namespace nghttp2 {
 
@@ -405,6 +406,15 @@ template <typename T, typename OutputIt> OutputIt utos(OutputIt dst, T n) {
   return res;
 }
 
+template <typename T>
+StringRef make_string_ref_uint(BlockAllocator &balloc, T n) {
+  auto iov = make_byte_ref(balloc, str_size("18446744073709551615") + 1);
+  auto p = iov.base;
+  p = util::utos(p, n);
+  *p = '\0';
+  return StringRef{iov.base, p};
+}
+
 template <typename T> std::string utos_unit(T n) {
   char u = 0;
   if (n >= (1 << 30)) {
diff --git a/src/util_test.cc b/src/util_test.cc
index 0a17e255..8a8ee181 100644
--- a/src/util_test.cc
+++ b/src/util_test.cc
@@ -239,8 +239,17 @@ void test_util_utos(void) {
 
   CU_ASSERT(("0" == StringRef{buf, util::utos(buf, 0)}));
   CU_ASSERT(("123" == StringRef{buf, util::utos(buf, 123)}));
-  CU_ASSERT(("9223372036854775808" ==
-             StringRef{buf, util::utos(buf, 9223372036854775808ULL)}));
+  CU_ASSERT(("18446744073709551615" ==
+             StringRef{buf, util::utos(buf, 18446744073709551615ULL)}));
+}
+
+void test_util_make_string_ref_uint(void) {
+  BlockAllocator balloc(1024, 1024);
+
+  CU_ASSERT("0" == util::make_string_ref_uint(balloc, 0));
+  CU_ASSERT("123" == util::make_string_ref_uint(balloc, 123));
+  CU_ASSERT("18446744073709551615" ==
+            util::make_string_ref_uint(balloc, 18446744073709551615ULL));
 }
 
 void test_util_utos_unit(void) {
diff --git a/src/util_test.h b/src/util_test.h
index f51692aa..b44d5b17 100644
--- a/src/util_test.h
+++ b/src/util_test.h
@@ -45,6 +45,7 @@ void test_util_http_date(void);
 void test_util_select_h2(void);
 void test_util_ipv6_numeric_addr(void);
 void test_util_utos(void);
+void test_util_make_string_ref_uint(void);
 void test_util_utos_unit(void);
 void test_util_utos_funit(void);
 void test_util_parse_uint_with_unit(void);