--- zlib-1.2.8/gzguts.h	2013-04-13 21:04:06.000000000 -0400
+++ gzguts.h	2014-07-17 13:35:54.000000000 -0400
@@ -207,3 +207,7 @@
 unsigned ZLIB_INTERNAL gz_intmax OF((void));
 #  define GT_OFF(x) (sizeof(int) == sizeof(z_off64_t) && (x) > gz_intmax())
 #endif
+
+#ifndef _WIN32
+#  include <unistd.h>
+#endif