Resizing without height defaults to 150px height

I am trying to resize the images to 1000px width without changing the height and keep the proportions.

In the Aqua resizer docs it says you can only give a width without height. But if i am doing this:

$resize_image_url = acf_photo_gallery_resize_image($full_image_url, 1000)

i get images that are 1000px wide and 150px in height.