diff --git a/builtin.c b/builtin.c
index d7b2337..239a258 100644
--- a/builtin.c
+++ b/builtin.c
@@ -2096,6 +2096,8 @@ do_systime(int nargs ATTRIBUTE_UNUSED)
 	return make_number((AWKNUM) lclock);
 }
 
+#ifndef HAVE_TIMEGM
+
 /* mktime_tz --- based on Linux timegm man page */
 
 static time_t
@@ -2124,6 +2126,14 @@ mktime_tz(struct tm *tm, const char *tzreq)
 	return ret;
 }
 
+static inline time_t
+timegm(struct tm *tm)
+{
+	return mktime_tz(tm, "UTC+0");
+}
+
+#endif /* HAVE_TIMEGM */
+
 /* do_mktime --- turn a time string into a timestamp */
 
 NODE *
@@ -2184,7 +2194,7 @@ do_mktime(int nargs)
 	then.tm_year = year - 1900;
 	then.tm_isdst = dst;
 
-	then_stamp = (do_gmt ? mktime_tz(& then, "UTC+0") : mktime(& then));
+	then_stamp = (do_gmt ? timegm(& then) : mktime(& then));
 	return make_number((AWKNUM) then_stamp);
 }
 
diff --git a/configure.ac b/configure.ac
index c6c7e50..bbc87b9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -312,7 +312,7 @@ AC_CHECK_FUNCS(__etoa_l atexit btowc fmod gai_strerror \
 	memset_ulong mkstemp posix_openpt setenv setlocale setsid sigprocmask \
 	snprintf strchr \
 	strerror strftime strcasecmp strncasecmp strcoll strtod strtoul \
-	system tmpfile towlower towupper tzset usleep waitpid wcrtomb \
+	system timegm tmpfile towlower towupper tzset usleep waitpid wcrtomb \
 	wcscoll wctype)
 dnl this check is for both mbrtowc and the mbstate_t type, which is good
 AC_FUNC_MBRTOWC