How tell pyinstaller what version of python to use?

So I have a small python program which I'd like to make a executable of using pyinstaller, the problem(?) I am having is that whenever I run the command "pyinstaller example.py" in the cmd prompt (windows 7), it automaticly uses python34. (I'd like it to use python27)

My question would be, how do I tell pyinstaller which python version to use?