Problem with Thai fonts in InDesign 15.0.1

Thai uses stress marks above letters to change the sound and/or meaning of words. A letter can use more than one of these stress marks, which are stacked. InDesign is putting them all in the same place above the letter, one on top of the other instead of stacking them so that they can all be seen. The only way I've been able to get around it is to create a new text box with only the stress mark in it which I then place properly above the letter. Is there any other way to do this?