How can I merge two commits into one if I already started rebase?

I am trying to merge 2 commits into 1, so I followed “squashing commits with rebase” from git ready.

I ran

git rebase --interactive HEAD~2

In the resulting editor, I change pick to squash and then save-quit, but the rebase fails with the error

Cannot ‘squash’ without a previous commit

Now that my work tree has reached this state, I’m having trouble recovering.

The command git rebase --interactive HEAD~2 fails with:

Interactive rebase already started

and git rebase --continue fails with

Cannot ‘squash’ without a previous commit