GIT help

[Rune Zedeler]

Because I by mistake did a merge of the master into dev/rune before the 
last time I pushed to git.sv.gnu.org, I undid these changed in my local 
branch before making my new changes locally.
But now, if I do

$ git push -f ssh+git://address@hidden/srv/git/lilypond.git/ 
dev/rune:dev/rune

Then git replies

error: denying non-fast forward refs/heads/dev/rune (you should pull first)
ng refs/heads/dev/rune non-fast forward

- and the push is not done.
I totally don't understand this - I thought that this was what the -f 
was for.
I am afraid that my old mistaken changes (that is, the merge with master 
branch) will be merged into my new changes if I do what it tells me, and 
do a pull.

Help!

-Rune