Git diff between current branch and master but not including unmerged master commits

I want a diff of all changes in a branch that is not merged to master yet.

I tried:

git diff master
git diff branch..master
git diff branch...master

However, in each of these cases the diff contains content in master that has not been merged into my branch yet.

Is there a way to do a diff between my branch and master that excludes changes in master that have not been merged into my branch yet?