diff --git a/tests/test_acmc.py b/tests/test_acmc.py
index f1447ad04be4ebd6c270dbaf7853c021302989df..34376c937beb1f593c1d9c62b30cc8cad3044e7d 100644
--- a/tests/test_acmc.py
+++ b/tests/test_acmc.py
@@ -233,6 +233,8 @@ def test_diff(tmp_dir, monkeypatch, caplog):
                 "diff",
                 "-d",
                 str(phen_path.resolve()),
+                "-od",
+                str(phen_path.resolve()),
                 "-ov",
                 "0.0.1",
             ],
@@ -279,6 +281,8 @@ def test_diff(tmp_dir, monkeypatch, caplog):
                 "diff",
                 "-d",
                 str(phen_path.resolve()),
+                "-od",
+                str(phen_path.resolve()),
                 "-ov",
                 "0.0.1",
             ],