Amazon lookup fails with 'cURL had HTTP failures'

[JonTabor]

Running on OpenBSD 6.0. I recently updated to the latest git version, after not having used this for about a year. When attempting to lookup on Amazon (US & UK tried) using any field, I get the following:

Error: cURL had HTTP failures (https://www.amazon.com/exec/obidos/external-search?index=books&keyword=Live+Free+Or+Die&page=1), error: 0

EDIT: This appears to be either an issue with OpenBSD's httpd, or a configuration issue; running it on Raspbian/nginx works as expected. I suspect running it on OpenBSD under nginx or lighttpd will also work as expected. I'll do more testing and report back.