git push - Git prevents pushing after amending a commit

Question

Usually, I just run

git add file
git commit
git push

but if I amend the commit before pushing it (with git commit --amend), the next push fails with

hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

How can I let git push the changes without merging branches? I only have one branch (master) and I'm the only person using this repo so why is it saying this?

git branch -a:

* master
  remotes/origin/HEAD -> origin/master
  remotes/origin/master

EDIT: Using gitk HEAD @{u}, I see that I have 2 branches, one with the original commit and another with the amended commit.

Answer 1

This should only be the case if you're amending an already-pushed commit. Generally you should never do that as you're then modifying published history. In your case however, you should be able to get away with push -f, which will overwrite the remote commit with your amended revision.