diff --git a/compat/mingw.c b/compat/mingw.c
index 0444d14b60316b..abcfde491b007a 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1091,6 +1091,7 @@ int pipe(int filedes[2])
 	return 0;
 }
 
+#ifndef __MINGW64__
 struct tm *gmtime_r(const time_t *timep, struct tm *result)
 {
 	if (gmtime_s(result, timep) == 0)
@@ -1104,6 +1105,7 @@ struct tm *localtime_r(const time_t *timep, struct tm *result)
 		return result;
 	return NULL;
 }
+#endif
 
 char *mingw_strbuf_realpath(struct strbuf *resolved, const char *path)
 {
diff --git a/git-compat-util.h b/git-compat-util.h
index 9eaae0a316b8e9..5cc6b125dbaa93 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -135,7 +135,9 @@
 /* Approximation of the length of the decimal representation of this type. */
 #define decimal_length(x)	((int)(sizeof(x) * 2.56 + 0.5) + 1)
 
-#if defined(__sun__)
+#ifdef __MINGW64__
+#define _POSIX_C_SOURCE 1
+#elif defined(__sun__)
  /*
   * On Solaris, when _XOPEN_EXTENDED is set, its header file
   * forces the programs to be XPG4v2, defeating any _XOPEN_SOURCE