bzr builddeb --native complains if the package number suggests a non-native package

example-local-0.4.2 contains a debianized source tree (built with bzr-builder, but that's not too important here) with a version of "0.4.2-654+24" or similar. I want to build it into a source package, but that builddeb won't let me:

mwh@grond:building-packages-on-launchpad$ bzr builddeb -S --native example-local-0.4.2/
Building using working tree
Running in native mode
Purging the build dir: ../build-area/bzr-git-0.4.2
Building the package in ../build-area/bzr-git-0.4.2, using debuild -S
This package has a Debian revision number but there does not seem to be
an appropriate original tar file or .orig directory in the parent directory;
(expected one of bzr-git_0.4.2.orig.tar.gz, bzr-git_0.4.2.orig.tar.bz2,
bzr-git_0.4.2.orig.tar.lzma or bzr-git-0.4.2.orig)
continue anyway? (y/n)