I'm trying to create a WP query to search a Custom post type by its title. By using the following code, I get all portfolio posts:

$search_query = array(
    'post_type' => 'portfolio',
    'posts_per_page' => 9,
    'paged' => $paged,
    'post_status' => 'publish'
);

If I add the 's' parameter to the query ($search_query['s'] = $keyword;), it ignores the 'post_type' and returns blog posts instead of portfolio posts.