gitignore: how to exclude a directory tree from being ignored

Hi I want to exclude binaries except in a dir tree that I do not control.

In .gitignore  I have:

!vendor/ *.exe *.o

I would expect that all *.exe and *.o are ignored except those somewhere in the vendor dir tree. However, the *.exe and *.o in the vendor dir tree are also ignored.

What is wrong ? Thanks for you help P