diff --git a/script_umdp3_checker/umdp3_conformance.py b/script_umdp3_checker/umdp3_conformance.py
index c2ae613a..64c85b6b 100644
--- a/script_umdp3_checker/umdp3_conformance.py
+++ b/script_umdp3_checker/umdp3_conformance.py
@@ -489,7 +489,8 @@ def print_in_box_b(
 def which_cms_is_it(path: str, print_volume: int = 3) -> CMSSystem:
     """Determine which CMS is in use based on the presence of certain files."""
     repo_path = Path(path)
-    if (repo_path / ".git").is_dir():
+    if (repo_path / ".git").exists():
+        # valid for a repo, worktree, or submodule
         cms = GitBdiffWrapper(repo_path)
     elif (repo_path / ".svn").is_dir():
         """