nginx : HTTP2 switch to HTTP (testing)

For testing purpose, I have been trying to switch my nginx server back to HTTP. I've been using HTTP2 since it was first available (release 1.9.5).

According to the documentation and this release note, HTTP2 is enabled simply by setting http2 is the listen directive in my serverblock.

However, it appears that removing "http2" doesn't force the server to use HTTP again.

Thoughts ?

Environment: Debian 8.5, nginx 1.11.1 compiled with LibreSSL 2.3.8

Thank you.