diff --git a/setup_main_tex_file.py b/setup_main_tex_file.py
index be8b295..b0ffe7d 100755
--- a/setup_main_tex_file.py
+++ b/setup_main_tex_file.py
@@ -149,6 +149,7 @@ def git_integration(func):
                     master_head = commit_into_master(master_add_paths, repo, comment)
                 else:
                     master_head = repo.revparse_single('refs/heads/master')
+            branch_ref = repo.references[f'refs/heads/{branch_name}']
             if master_head not in repo.walk(branch_ref.target):
                 merge_master_into_branch(master_head, branch_name, repo)