diff --git a/tests/_support_data/gen-data.sh b/tests/_support_data/gen-data.sh
index 1c6569d..24bee5f 100755
--- a/tests/_support_data/gen-data.sh
+++ b/tests/_support_data/gen-data.sh
@@ -21,6 +21,7 @@ do
 	echo ">> $repo"
 	cd $repo
 	for i in $(git for-each-ref --format="%(refname:short)" --no-merged=origin/HEAD refs/remotes/origin); do git switch --track $i; done
+	git branch -D test-head || true
 	cd ..
 done
 # recover submodules to initial state (branches will remain)