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
@@ -111,7 +111,12 @@
 	ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
 	if ((gidlist = malloc(sizeof(gid_t) * ngroups_max)) == NULL)
 		err(1, "malloc");
-	for (gids = 0;
+	/* Populate the egid slot in our groups to avoid accidents. */
+	if (gid == 0)
+		gidlist[0] = getegid();
+	else
+		gidlist[0] = gid;
+	for (gids = 1;
 	    (p = strsep(&grouplist, ",")) != NULL && gids < ngroups_max; ) {
 		if (*p == '\0')
 			continue;