diff -urN 3/lib/userspec.c 4/lib/userspec.c
--- 3/lib/userspec.c	2004-10-05 17:42:29.000000000 +0000
+++ 4/lib/userspec.c	2005-03-30 14:56:20.000000000 +0000
@@ -264,7 +264,7 @@
   char const *error_msg =
     parse_with_separator (spec, colon, uid, gid, username, groupname);
 
-  if (!colon && error_msg)
+  if (!colon && error_msg && (!getenv("POSIXLY_CORRECT") || posix2_version() < 200112))
     {
       /* If there's no colon but there is a dot, and if looking up the
 	 whole spec failed (i.e., the spec is not a owner name that
@@ -273,6 +273,13 @@
 	 the POSIX-required behavior is always tried first.  */
 
       char const *dot = strchr (spec, '.');
+
+      if (dot)
+        {
+	  if (! posix2_version() < 200112)
+	    error (0,0,_("`%s' syntax is obsolete; use `:' since this will be removed in future"), spec);
+	}
+
       if (dot
 	  && ! parse_with_separator (spec, dot, uid, gid, username, groupname))
 	error_msg = NULL;