diff --git a/server/autotest_server/testers/py/setup.py b/server/autotest_server/testers/py/setup.py
index d781e244..724fb8fb 100644
--- a/server/autotest_server/testers/py/setup.py
+++ b/server/autotest_server/testers/py/setup.py
@@ -31,6 +31,10 @@ def settings():
     prop = components["PyTestData"]["properties"]["output_verbosity"]
     if "anyOf" in prop:
         prop["enum"] = [v for sub in prop.pop("anyOf") for v in sub["enum"]]
+    # The runtime default "" is a fall-back sentinel that is not a valid choice in
+    # either tester branch of the dependencies block; dropping it lets the form
+    # apply the branch default instead.
+    prop.pop("default", None)
 
     # Inject dependencies for output_verbosity for JSON Schema form
     json_schema["properties"]["test_data"]["items"]["dependencies"] = {
diff --git a/server/autotest_server/tests/testers/test_schema.py b/server/autotest_server/tests/testers/test_schema.py
index 9d666497..c10f3c87 100644
--- a/server/autotest_server/tests/testers/test_schema.py
+++ b/server/autotest_server/tests/testers/test_schema.py
@@ -68,3 +68,17 @@ def test_valid_simple_schema(tester, files_list):
         instance = json.load(f)
 
     jsonschema.validate(instance, schema)
+
+
+def test_py_output_verbosity_defaults_match_tester_branches():
+    """A base default that no dependencies branch accepts leaves new test groups
+    invalid in the settings form (MarkUsProject/Markus#8129)."""
+    schemas, definitions = get_settings()
+    prop = definitions["PyTestData"]["properties"]["output_verbosity"]
+    branches = schemas["py"]["properties"]["test_data"]["items"]["dependencies"]["tester"]["oneOf"]
+    branch_enums = [branch["properties"]["output_verbosity"]["enum"] for branch in branches]
+    if "default" in prop:
+        assert any(prop["default"] in enum for enum in branch_enums)
+    for branch in branches:
+        verbosity = branch["properties"]["output_verbosity"]
+        assert verbosity["default"] in verbosity["enum"]