adding current_page_parent for a page displaying custom post type

Hi,
I’m doing a small-business site and have 2 kinds of posts: blog posts and products (created as custom post type) and have these 2 pages in navigation menu: Blog and Products.
The Blog page is displaying blog posts with index.php file, and Products page is displaying product posts with products.php template file.

Now it doesn’t matter if I view post or product- it’s always the Blog page that’s getting current_page_parent css class (I reckon it has sth to do with “Posts page: Blog” being selected in Reading Settings in admin).

I would like to have that class in menu for Blog when viewing blog posts, and for Products when viewing products.

Please help.