=item <upstream-commit-ish>
The new upstream branch (or commit-ish).
-Default is C<upstream>.
+The default is to look for one of these tags, in this order:
+U vU upstream/U;
+where U is the new upstream version.
+(This is the same algorithm as L<git-deborig(1)>.)
It is a snag if the upstream contains a debian/ directory;
if forced to proceed,
make-patches will fail with exit status 7,
and an error message.
(The message can be suppress with --quiet-would-amend.)
+If the problem is simply that
+the existing patches were not made by git-debrebase,
+using dgit quilt-fixup instead should succeed.
=item git-debrebase convert-from-gbp [<upstream-commit-ish>]