Index: usr.sbin/chown/chown.c
===================================================================
--- usr.sbin/chown/chown.c
+++ usr.sbin/chown/chown.c
@@ -55,6 +55,7 @@
 #include <libgen.h>
 #include <pwd.h>
 #include <signal.h>
+#include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -64,7 +65,7 @@
 static void    a_gid(const char *);
 static void    a_uid(const char *);
 static void    chownerr(const char *);
-static uid_t   id(const char *, const char *);
+static id_t    id(const char *, const char *);
 static void    usage(void);
 static void    print_info(const FTSENT *, int);

@@ -243,19 +244,16 @@
        uid = ((pw = getpwnam(s)) != NULL) ? pw->pw_uid : id(s, "user");
 }

-static uid_t
+static id_t
 id(const char *name, const char *type)
 {
-       uid_t val;
+       unsigned long val;
        char *ep;

-       /*
-        * XXX
-        * We know that uid_t's and gid_t's are unsigned longs.
-        */
        errno = 0;
        val = strtoul(name, &ep, 10);
-       if (errno || *ep != '\0')
+       _Static_assert(UID_MAX == GID_MAX, "UID and GID MAXes differ");
+       if (errno || *ep != '\0' || (val > UID_MAX))
                errx(1, "%s: illegal %s name", name, type);
        return (val);
 }