Can't connect to anything with Gun adapter using HTTP proxy

[howaboutlollmao]

Tesla and Gun both with latest commits from master branch, but the same can be seen with Tesla 1.4.4 and Gun 2.0.0-rc1.

gun_client = Tesla.client([], Tesla.Adapter.Gun)
Tesla.get(gun_client, "http://icanhazip.com", opts: [adapter: [timeout: 3_000, proxy: {{127, 0, 0, 1}, 8118}]])

Running this in IEX returns {:error, :recv_response_timeout} no matter what the URL is. SOCKS proxies work fine, the problem is only with HTTP.
ninenines/gun#300 might be related, since the symptoms are similar (connection is created, but no request to end server is made).