apache mod_rewrite, trailing slash, serveralias

Hello,

I've run into a problem with the subject. Sorry if this was answered -
I could not find it.

I have both wap and www sites in the same VirtualHost entry, and a
simple
rewrite rule:

<VirtualHost *>
<Directory /var/www/vhosts/site>
AllowOverride All
Options FollowSymLinks Includes
Order allow,deny
Allow from all
</Directory>
DocumentRoot /var/www/vhosts/site
ServerName site.com
ServerAlias wap.site.com
RewriteEngine on
# wap site is in /wap/ directory
RewriteCond %{HTTP_HOST} ^wap\.site\.com$
RewriteRule ^/(.*)$ /wap/$1
</VirtualHost>

Everything works nicely, except one thing: when I access url like
wap.site.com/dir (without slash), it gets redirected to site.com/dir/
instead of site.com/wap/dir

I can fix this by splitting Virtual host into two, one for site.com
and one for wap.site.com. But maybe there is a (simple) way to fix
this?

Thanks a lot

Alex