--- ruby-2.3.0/include/ruby/win32.h.orig	2015-09-12 14:23:22.000000000 +0900
+++ ruby-2.3.0/include/ruby/win32.h	2016-02-13 19:58:24.481681300 +0900
@@ -715,8 +715,10 @@
 
 int rb_w32_times(struct tms *);
 
+#ifndef __MINGW64_VERSION_MAJOR
 struct tm *gmtime_r(const time_t *, struct tm *);
 struct tm *localtime_r(const time_t *, struct tm *);
+#endif
 
 /* thread stuff */
 int  rb_w32_sleep(unsigned long msec);
--- ruby-2.3.0/win32/win32.c.orig	2015-12-01 13:25:06.000000000 +0900
+++ ruby-2.3.0/win32/win32.c	2016-02-13 19:58:24.495683100 +0900
@@ -7542,6 +7542,7 @@
 # define localtime_s _localtime64_s
 #endif
 
+#ifndef __MINGW64_VERSION_MAJOR
 /* License: Ruby's */
 struct tm *
 gmtime_r(const time_t *tp, struct tm *rp)
@@ -7589,6 +7590,7 @@
 #endif
     return rp;
 }
+#endif
 
 /* License: Ruby's */
 int
