Git -- non-fast-forward updates were rejected

I got the following error message:

To prevent you from losing history, non-fast-forward updates were rejected
Merge the remote changes before pushing again.  See the 'Note about
fast-forwards' section of 'git push --help' for details.

Stackoverflow helped, as usual. As I am the sole developer of my can of worms, I just added the '-f' flag. It's nice to do the last commit of the photometry code which I've been working on for the last 3 months.