diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 5a74954..35cef26 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -2,6 +2,9 @@
 
 test_description='test git worktree add'
 
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
 . ./test-lib.sh
 
 . "$TEST_DIRECTORY"/lib-rebase.sh