node-postgres: Regression in 7.18.0 causing "unsupported frontend protocol 1234.5679: server supports 2.0 to 3.0"

I don’t use pg directly but through sequelize (ORM). Updating to 7.17.0 works fine. 7.17.1 works fine, but the same unchanged code with pg 7.18.0 will throw an exception on connection:

unsupported frontend protocol 1234.5679: server supports 2.0 to 3.0

I don’t have the full exception atm but this bit:

at Connection.connectingErrorHandler (C:\Users\jant\Repos\get-coffee\packages\get-coffee-api\node_modules\pg\lib\client.js:194:14)
    at Connection.emit (events.js:210:5)
    at Connection.EventEmitter.emit (domain.js:476:20)
    at TLSSocket.<anonymous> (C:\Users\jant\Repos\get-coffee\packages\get-coffee-api\node_modules\pg\lib\connection.js:144:12)
    at TLSSocket.emit (events.js:210:5)
    at TLSSocket.EventEmitter.emit (domain.js:476:20)
    at addChunk (_stream_readable.js:308:12)
    at readableAddChunk (_stream_readable.js:289:11)
    at TLSSocket.Readable.push (_stream_readable.js:223:10)
    at TLSWrap.onStreamRead (internal/stream_base_commons.js:182:23)

Why do I believe this is a regression: After downgrading to 7.17.1, connection works fine. After upgrading to 7.18.0, it breaks again.