I have a fork of an old, not-very-well-supported repository. In the fork, whenever I create a pull request from feature branch to master (i.e. the default branch), I have to specify base repository manually, every single time:

There's a similar issue with BitBucket; it has a well description, but the answers are out of scope for this one.
Can I change this behavior of GitHub UI somehow, so that new pull requests are created against specific repository?
I assume that I can achieve this by de-forking the repo, but I'd like to keep the fork relation a) due to historical reasons, b) out of respect to the original author, and c) because this is a highly error-prone process for now (there's no single button for that, unfortunately)