--- etc/c/zlib/gzlib.c.orig	2018-10-19 22:37:53.000000000 +0900
+++ etc/c/zlib/gzlib.c	2018-11-10 21:40:01.000000000 +0900
@@ -3,6 +3,7 @@
  * For conditions of distribution and use, see copyright notice in zlib.h
  */
 
+#include <unistd.h>
 #include "gzguts.h"
 
 #if defined(_WIN32) && !defined(__BORLANDC__) && !defined(__MINGW32__) && !defined(__DMC__)
