"Wrong type argument: number-or-marker-p"

The same happens if I type C-c C-o on the link.  This is mapped to org-open-at-point, which should handle internal links.

However, if I type C-c o on the link, then the cursor goes to the anchor.  This is mapped to org-open-at-point-global, which the org info help says is undefined on internal links.

This behavior is new, I believe since the last org package update.  I'm currently on org mode version 9.1.2.