problem with wp_rewrite

I’ve got an issue i can’t wrap my head around. I am using wp_rewrite to set up some custom rewrite rules. I’m using the following rule

$newrules[‘^mybasetag/([-A-Za-z0-9])$’] = ‘index.php?pagename=$matches[1]&kw=$matches[2]’;

It seems to be mostly working fine. i can go to https://mysite.com/mybasetag/123 and everything works fine. If i switch the 123 at the end of the url to anything non-numeric the page fails. I’m not sure what I am doing wrong? Can anyone help?