diff --git a/tests/scm_mock.py b/tests/scm_mock.py
index ede857327..411db9116 100644
--- a/tests/scm_mock.py
+++ b/tests/scm_mock.py
@@ -18,6 +18,7 @@ import scm
 
 
 def GIT(test: unittest.TestCase,
+        *,
         branchref: str | None = None):
     """Installs fakes/mocks for scm.GIT so that: