Tried that, but it got through for me:
git commit --amend
*just closed the editor that popped up* No modified files, so no updates needed. [detached HEAD f75c04d] Made it more explicit that we avoid yielding in bad places. 3 files changed, 55 insertions(+), 17 deletions(-)
I closed the editor instead of saying -C HEAD, but that shouldn't matter. I think the problem is "No modified files, so no updates needed."