Cannot upload 14MB file

The Files field on an issue says you can upload files up to 50MB.

However, today I have been unable to upload a 14MB PDF file. I tried it on a couple of issues (in case it was blocked on an issue that already had several uploaded large-ish files), and I got this error:

413 Request Entity Too Large


Source: https://www.drupal.org/project/issues/rss/infrastructure