diff --git a/usr.sbin/chroot/chroot.c b/usr.sbin/chroot/chroot.c
--- a/usr.sbin/chroot/chroot.c
+++ b/usr.sbin/chroot/chroot.c
@@ -34,6 +34,7 @@
 
 #include <ctype.h>
 #include <err.h>
+#include <errno.h>
 #include <grp.h>
 #include <limits.h>
 #include <paths.h>
@@ -46,17 +47,59 @@
 
 static void usage(void) __dead2;
 
+static gid_t
+resolve_group(const char *group)
+{
+	struct group *gp;
+
+	gp = getgrnam(group);
+	if (gp == NULL) {
+		char *endp;
+		unsigned long gid;
+
+		errno = 0;
+		gid = strtoul(group, &endp, 0);
+		if (errno == 0 && *endp == '\0')
+			gp = getgrgid(gid);
+	}
+
+	if (gp == NULL)
+		errx(1, "no such group '%s'", group);
+
+	return (gp->gr_gid);
+}
+
+static uid_t
+resolve_user(const char *user)
+{
+	struct passwd *pw;
+
+	pw = getpwnam(user);
+	if (pw == NULL) {
+		char *endp;
+		unsigned long uid;
+
+		errno = 0;
+		uid = strtoul(user, &endp, 0);
+		if (errno == 0 && *endp == '\0')
+			pw = getpwuid(uid);
+	}
+
+	if (pw == NULL)
+		errx(1, "no such user '%s'", user);
+
+	return (pw->pw_uid);
+}
+
 int
 main(int argc, char *argv[])
 {
-	struct group	*gp;
-	struct passwd	*pw;
-	char		*endp, *p, *user, *group, *grouplist;
-	const char	*shell;
+	const char	*group, *p, *shell, *user;
+	char		*grouplist;
+	long		ngroups_max;
 	gid_t		gid, *gidlist;
 	uid_t		uid;
 	int		arg, ch, error, gids;
-	long		ngroups_max;
 	bool		nonprivileged;
 
 	gid = 0;
@@ -94,19 +137,8 @@
 	if (argc < 1)
 		usage();
 
-	if (group != NULL) {
-		if (isdigit((unsigned char)*group)) {
-			gid = (gid_t)strtoul(group, &endp, 0);
-			if (*endp != '\0')
-				goto getgroup;
-		} else {
- getgroup:
-			if ((gp = getgrnam(group)) != NULL)
-				gid = gp->gr_gid;
-			else
-				errx(1, "no such group `%s'", group);
-		}
-	}
+	if (group != NULL)
+		gid = resolve_group(group);
 
 	ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
 	if ((gidlist = malloc(sizeof(gid_t) * ngroups_max)) == NULL)
@@ -121,35 +153,13 @@
 		if (*p == '\0')
 			continue;
 
-		if (isdigit((unsigned char)*p)) {
-			gidlist[gids] = (gid_t)strtoul(p, &endp, 0);
-			if (*endp != '\0')
-				goto getglist;
-		} else {
- getglist:
-			if ((gp = getgrnam(p)) != NULL)
-				gidlist[gids] = gp->gr_gid;
-			else
-				errx(1, "no such group `%s'", p);
-		}
-		gids++;
+		gidlist[gids++] = resolve_group(p);
 	}
 	if (p != NULL && gids == ngroups_max)
 		errx(1, "too many supplementary groups provided");
 
-	if (user != NULL) {
-		if (isdigit((unsigned char)*user)) {
-			uid = (uid_t)strtoul(user, &endp, 0);
-			if (*endp != '\0')
-				goto getuser;
-		} else {
- getuser:
-			if ((pw = getpwnam(user)) != NULL)
-				uid = pw->pw_uid;
-			else
-				errx(1, "no such user `%s'", user);
-		}
-	}
+	if (user != NULL)
+		uid = resolve_user(user);
 
 	if (nonprivileged) {
 		arg = PROC_NO_NEW_PRIVS_ENABLE;