diff --git a/tests/app/conftest.py b/tests/app/conftest.py
index 3706494f2..c8f06e8c4 100644
--- a/tests/app/conftest.py
+++ b/tests/app/conftest.py
@@ -603,7 +603,7 @@ def sample_letter_notification(sample_letter_template):
         'address_line_6': 'A6',
         'postcode': 'A_POST'
     }
-    return create_notification(sample_letter_template, personalisation=address)
+    return create_notification(sample_letter_template, reference='foo', personalisation=address)
 
 
 @pytest.fixture(scope='function')