diff --git a/src/timegm.c b/src/timegm.c
index 62b14430..e52fe74a 100644
--- a/src/timegm.c
+++ b/src/timegm.c
@@ -53,3 +53,36 @@ time_t nghttp2_timegm(struct tm *tm) {
 
   return (time_t)t;
 }
+
+/* Returns nonzero if the |y| is the leap year. The |y| is the year,
+   including century (e.g., 2012) */
+static int is_leap_year(int y) {
+  return y % 4 == 0 && (y % 100 != 0 || y % 400 == 0);
+}
+
+/* The number of days before ith month begins */
+static int daysum[] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
+
+time_t nghttp2_timegm_without_yday(struct tm *tm) {
+  int days;
+  int num_leap_year;
+  int64_t t;
+  if (tm->tm_mon > 11) {
+    return -1;
+  }
+  num_leap_year = count_leap_year(tm->tm_year + 1900) - count_leap_year(1970);
+  days = (tm->tm_year - 70) * 365 + num_leap_year + daysum[tm->tm_mon] +
+         tm->tm_mday - 1;
+  if (tm->tm_mon >= 2 && is_leap_year(tm->tm_year + 1900)) {
+    ++days;
+  }
+  t = ((int64_t)days * 24 + tm->tm_hour) * 3600 + tm->tm_min * 60 + tm->tm_sec;
+
+#if SIZEOF_TIME_T == 4
+  if (t < INT32_MIN || t > INT32_MAX) {
+    return -1;
+  }
+#endif /* SIZEOF_TIME_T == 4 */
+
+  return t;
+}
diff --git a/src/timegm.h b/src/timegm.h
index 4168fdd1..4383fda1 100644
--- a/src/timegm.h
+++ b/src/timegm.h
@@ -39,6 +39,11 @@ extern "C" {
 
 time_t nghttp2_timegm(struct tm *tm);
 
+/* Just like nghttp2_timegm, but without using tm->tm_yday.  This is
+   useful if we use tm from strptime, since some platforms do not
+   calculate tm_yday with that call. */
+time_t nghttp2_timegm_without_yday(struct tm *tm);
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */
diff --git a/src/util.cc b/src/util.cc
index 191bd13f..9586ab77 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -354,7 +354,7 @@ time_t parse_http_date(const std::string &s) {
   if (r == 0) {
     return 0;
   }
-  return nghttp2_timegm(&tm);
+  return nghttp2_timegm_without_yday(&tm);
 }
 
 namespace {