diff --git a/share/man/man9/ioctl.9 b/share/man/man9/ioctl.9
index 5c472b078d09..d5c017468cd8 100644
--- a/share/man/man9/ioctl.9
+++ b/share/man/man9/ioctl.9
@@ -1,4 +1,4 @@
-.\" $NetBSD: ioctl.9,v 1.10 2001/09/10 23:36:57 wiz Exp $
+.\" $NetBSD: ioctl.9,v 1.11 2001/09/13 17:19:55 atatat Exp $
 .\"
 .\" Copyright (c) 1999  The NetBSD Foundation, Inc.
 .\" All rights reserved.
@@ -61,6 +61,9 @@ system call. E.g. ioctl(s,FOOIOCTL,...)
 .It Fn fun
 a macro which can be one of
 .Bl -tag -width _IOWR
+.It _IO
+the call is a simple message to the kernel by itself.  It does not copy
+anything into the kernel, nor does it want anything back.
 .It _IOR
 the call only reads parameters from the kernel and does not
 pass any to it