--- udunits/udunits.c.orig	2009-01-06 02:01:44.000000000 +0900
+++ udunits/udunits.c	2020-11-22 10:37:24.000000000 +0900
@@ -7,6 +7,7 @@
 #ifndef _XOPEN_SOURCE
 #  define _XOPEN_SOURCE 500
 #endif
+#include <unistd.h>
 #include <limits.h>	/* for _POSIX_MAX_INPUT */
 #include <stddef.h>	/* for size_t */
 #include <stdio.h>	/* for I/O functions, and NULL */
@@ -90,7 +91,7 @@
 }
 
 
-main(argc, argv)
+int main(argc, argv)
     int			argc;
     char		**argv;
 {