diff --git a/usr.sbin/chown/chown.c b/usr.sbin/chown/chown.c
index b0154588846e..88311d7f98c2 100644
--- a/usr.sbin/chown/chown.c
+++ b/usr.sbin/chown/chown.c
@@ -145,6 +145,7 @@ main(argc, argv)
 		}
 #ifdef SUPPORT_DOT
 		else if ((cp = strchr(*argv, '.')) != NULL) {
+			warnx("seperation of user and group with a period is deprecated");
 			*cp++ = '\0';
 			a_gid(cp);
 		}