diff --git a/share/man/man5/ifconfig.if.5 b/share/man/man5/ifconfig.if.5
index 0ae247776239..47dc140d6f67 100644
--- a/share/man/man5/ifconfig.if.5
+++ b/share/man/man5/ifconfig.if.5
@@ -1,4 +1,4 @@
-.\"	$NetBSD: ifconfig.if.5,v 1.14 2010/09/26 18:52:04 apb Exp $
+.\"	$NetBSD: ifconfig.if.5,v 1.15 2011/04/07 00:22:59 jym Exp $
 .\"
 .\" Copyright (c) 1996 Matthew R. Green
 .\" All rights reserved.
@@ -24,7 +24,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd September 26, 2010
+.Dd April 7, 2011
 .Dt IFCONFIG.IF 5
 .Os
 .Sh NAME
@@ -56,6 +56,14 @@ variable or the
 file for the
 .Sy fxp0
 interface).
+Only characters allowed in
+.Xr sh 1
+variables names should be used for
+.Ar nnX
+.Po Xr ascii 7
+uppercase and lowercase letters, digits, and underscore
+.Pc .
+.Pp
 The variable or file will get evaluated only if the interface exists on
 the system.
 Multiple lines can be placed in a variable or file, and will be