diff --git a/src/timegm.c b/src/timegm.c
index b80e0789..62b14430 100644
--- a/src/timegm.c
+++ b/src/timegm.c
@@ -34,7 +34,7 @@ static int count_leap_year(int y) {
 }
 
 /* Based on the algorithm of Python 2.7 calendar.timegm. */
-time_t timegm(struct tm *tm) {
+time_t nghttp2_timegm(struct tm *tm) {
   int days;
   int num_leap_year;
   int64_t t;
diff --git a/src/timegm.h b/src/timegm.h
index 2624657a..4168fdd1 100644
--- a/src/timegm.h
+++ b/src/timegm.h
@@ -37,7 +37,7 @@ extern "C" {
 #include <time.h>
 #endif // HAVE_TIME_H
 
-time_t timegm(struct tm *tm);
+time_t nghttp2_timegm(struct tm *tm);
 
 #ifdef __cplusplus
 }
diff --git a/src/util.cc b/src/util.cc
index 2d7c7734..191bd13f 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -278,7 +278,7 @@ std::string common_log_date(time_t t) {
 #ifdef HAVE_STRUCT_TM_TM_GMTOFF
   auto gmtoff = tms.tm_gmtoff;
 #else  // !HAVE_STRUCT_TM_TM_GMTOFF
-  auto gmtoff = timegm(&tms) - t;
+  auto gmtoff = nghttp2_timegm(&tms) - t;
 #endif // !HAVE_STRUCT_TM_TM_GMTOFF
   if (gmtoff >= 0) {
     *p++ = '+';
@@ -326,7 +326,7 @@ std::string iso8601_date(int64_t ms) {
 #ifdef HAVE_STRUCT_TM_TM_GMTOFF
   auto gmtoff = tms.tm_gmtoff;
 #else  // !HAVE_STRUCT_TM_TM_GMTOFF
-  auto gmtoff = timegm(&tms) - sec;
+  auto gmtoff = nghttp2_timegm(&tms) - sec;
 #endif // !HAVE_STRUCT_TM_TM_GMTOFF
   if (gmtoff == 0) {
     *p++ = 'Z';
@@ -354,7 +354,7 @@ time_t parse_http_date(const std::string &s) {
   if (r == 0) {
     return 0;
   }
-  return timegm(&tm);
+  return nghttp2_timegm(&tm);
 }
 
 namespace {