diff --git a/lib/libc/locale/iswalnum.3 b/lib/libc/locale/iswalnum.3
index f00c9128d356..a31146b19c8a 100644
--- a/lib/libc/locale/iswalnum.3
+++ b/lib/libc/locale/iswalnum.3
@@ -1,4 +1,4 @@
-.\"	$NetBSD: iswalnum.3,v 1.4 2002/03/18 08:03:39 wiz Exp $
+.\"	$NetBSD: iswalnum.3,v 1.5 2002/07/10 14:46:10 yamt Exp $
 .\"
 .\" Copyright (c) 1991 The Regents of the University of California.
 .\" All rights reserved.
@@ -112,3 +112,6 @@ return non-zero if the character tests true.
 .Sh STANDARDS
 The functions conform to
 .St -isoC99 .
+.Sh CAVEATS
+The argument to these functions must be WEOF or valid wchar_t
+value with current locale; otherwise, the result is undefined.