diff --git a/mirror_to_github.sh b/mirror_to_github.sh
index 63d886b..36d2171 100755
--- a/mirror_to_github.sh
+++ b/mirror_to_github.sh
@@ -9,7 +9,10 @@ if [ ! -d .git ]; then
 fi
 touch git-marks1.txt git-marks2.txt
 [ -f git-authors.txt ] || echo 'lapo@lapo.it = Lapo Luchini <lapo@lapo.it>' > git-authors.txt
-mtn ls branches --ignore-suspend-certs | sort -V | awk -F . '{ print $0 " = " ($4 ? $4 : "trunk") }' > git-branches.txt
+mtn ls branches --ignore-suspend-certs | sort -V | awk '
+  NR == 1 { base = $0; len = length(base) }
+  { d = length($0) - len; print $0 " = " (d > 0 ? substr($0, len+2) : "trunk") }
+' > git-branches.txt
 mtn --quiet --authors=git-authors.txt --branches-file=git-branches.txt --import-marks=git-marks1.txt --export-marks=git-marks1.txt git_export | \
     git fast-import --import-marks=git-marks2.txt --export-marks=git-marks2.txt
 git push --mirror origin