debuild error please advise

["justin cunningham" <jcunningham@engine8.com>]

I'm using a debian package built by a friend and it works great however
I need a patch he didn't so he told me to get his source, apply my patch
then debuild.

So I downloaded his source package orig.tar.gz, .dsc, diff.gz
i386_changes -- basically all files except the .deb and extracted the
source, applied the patch and cd into the source tree and ran 'fakeroot
debuild' and got 

$ fakeroot debuild
debuild: fatal error at line 317:
Cannot find debian/rules anywhere!  Are you in the source code tree?

What did I do wrong?  Typically when I apply patches to src packages I
just patch them and use apt-get -b source package but the version in the
debian branch is way old.

regards, justin