custom div class sort 2 fields

Hello,

I’m trying to change the sort order to sort on to fields. When I update the orderby it only works for the first field. Any ideas why this won’t sort?

<div class="et_pb_row">

	<?php
		$args = array(
			'post_type'  => 'course',
			'child_of'   => 0,
			'orderby'    => 'course, post_title',
			'order'      => 'ASC',
			'hide_empty' => 0,
			'taxonomy'   => 'cat_course',
			'pad_counts' => false
                       );