diff --git a/src/shrpx-unittest.cc b/src/shrpx-unittest.cc
index 0de07c3d..42998acf 100644
--- a/src/shrpx-unittest.cc
+++ b/src/shrpx-unittest.cc
@@ -123,6 +123,7 @@ int main(int argc, char* argv[])
       !CU_add_test(pSuite, "util_quote_string",
                    shrpx::test_util_quote_string) ||
       !CU_add_test(pSuite, "util_utox", shrpx::test_util_utox) ||
+      !CU_add_test(pSuite, "util_http_date", shrpx::test_util_http_date) ||
       !CU_add_test(pSuite, "gzip_inflate", test_nghttp2_gzip_inflate)) {
      CU_cleanup_registry();
      return CU_get_error();
diff --git a/src/util.cc b/src/util.cc
index 8be0a949..14d58af6 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -163,17 +163,62 @@ std::string quote_string(const std::string& target)
   return res;
 }
 
+namespace {
+template<typename Iterator>
+Iterator cpydig(Iterator d, int n, size_t len)
+{
+  auto p = d + len - 1;
+
+  do {
+    *p-- = (n % 10) + '0';
+    n /= 10;
+  } while(p >= d);
+
+  return d + len;
+}
+} // namespace
+
+namespace {
+const char *MONTH[] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun",
+                        "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
+const char *DAY_OF_WEEK[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri",
+                              "Sat" };
+} // namespace
+
 std::string http_date(time_t t)
 {
-  char buf[32];
-  tm tms;
+  struct tm tms;
+  std::string res;
 
   if(gmtime_r(&t, &tms) == nullptr) {
-    return "";
+    return res;
   }
 
-  auto rv = strftime(buf, sizeof(buf), "%a, %d %b %Y %H:%M:%S GMT", &tms);
-  return std::string(&buf[0], &buf[rv]);
+  /* Sat, 27 Sep 2014 06:31:15 GMT */
+  res.resize(29);
+
+  auto p = std::begin(res);
+
+  auto s = DAY_OF_WEEK[tms.tm_wday];
+  p = std::copy(s, s + 3, p);
+  *p++ = ',';
+  *p++ = ' ';
+  p = cpydig(p, tms.tm_mday, 2);
+  *p++ = ' ';
+  s = MONTH[tms.tm_mon];
+  p = std::copy(s, s + 3, p);
+  *p++ = ' ';
+  p = cpydig(p, tms.tm_year + 1900, 4);
+  *p++ = ' ';
+  p = cpydig(p, tms.tm_hour, 2);
+  *p++ = ':';
+  p = cpydig(p, tms.tm_min, 2);
+  *p++ = ':';
+  p = cpydig(p, tms.tm_sec, 2);
+  s = " GMT";
+  p = std::copy(s, s + 4, p);
+
+  return res;
 }
 
 time_t parse_http_date(const std::string& s)
diff --git a/src/util_test.cc b/src/util_test.cc
index bc301399..54b18f92 100644
--- a/src/util_test.cc
+++ b/src/util_test.cc
@@ -118,4 +118,10 @@ void test_util_utox(void)
   CU_ASSERT("100000000" == util::utox(1LL << 32));
 }
 
+void test_util_http_date(void)
+{
+  CU_ASSERT("Thu, 01 Jan 1970 00:00:00 GMT" == util::http_date(0));
+  CU_ASSERT("Wed, 29 Feb 2012 09:15:16 GMT" == util::http_date(1330506916));
+}
+
 } // namespace shrpx
diff --git a/src/util_test.h b/src/util_test.h
index d0220a88..f4ffefc5 100644
--- a/src/util_test.h
+++ b/src/util_test.h
@@ -34,6 +34,7 @@ void test_util_to_base64(void);
 void test_util_percent_encode_token(void);
 void test_util_quote_string(void);
 void test_util_utox(void);
+void test_util_http_date(void);
 
 } // namespace shrpx