Git create branch where detached HEAD is

I tried something like this:

git branch temp

to create a new branch but don't move the HEAD. But I get:

# Not currently on any branch.

I don't want to merge anything, I just want a new branch at the current HEAD.

You're sitting on a detached HEAD:

git checkout <sha>

You want to make a branch at that commit:

git branch my-new-branch

And now switch to that branch:

git checkout my-new-branch