diff --git a/tools/schemacode/bidsschematools/data/tests/test_rules.py b/tools/schemacode/bidsschematools/data/tests/test_rules.py
index e8da90ee93..3eb11a6ed0 100644
--- a/tools/schemacode/bidsschematools/data/tests/test_rules.py
+++ b/tools/schemacode/bidsschematools/data/tests/test_rules.py
@@ -83,8 +83,7 @@ def test_rule_objects(schema_obj):
                 if object_type in ["extensions", "suffixes"]:
                     # Some object types are referenced via their "value" fields in the rules
                     object_values = [
-                        schema_obj["objects"][object_type][k]["value"]
-                        for k in schema_obj["objects"][object_type].keys()
+                        value["value"] for value in schema_obj["objects"][object_type].values()
                     ]
                 else:
                     # But other object types are referenced via their keys
@@ -100,7 +99,7 @@ def test_rule_objects(schema_obj):
 
     if not_found:
         not_found_string = "\n".join([f"{'.'.join(path)} == {val}" for path, val in not_found])
-        raise ValueError(not_found_string)
+        raise AssertionError(f"Undefined objects found in rules: {not_found_string}")
 
 
 @pytest.mark.validate_schema