WordPress database error You have an error in your SQL syntax

I have a very large error_log in root of my multi network site with Post indexer (this is a Guesstimate)
this is the error I'm getting

[25-Nov-2016 17:12:13 UTC] WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ''YEAR') < CURRENT_DATE() LIMIT 50' at line 1 for query SELECT BLOG_ID, ID FROM wp_network_posts WHERE DATE_ADD(post_date, INTERVAL 1 'YEAR') < CURRENT_DATE() LIMIT 50 made by do_action_ref_array, call_user_func_array, postindexercron->process_tidy_agedposts, postindexermodel->remove_posts_older_than

Using Maria DB v 10.1 as the error said

thanks
Mitch