diff --git a/bin/config.py b/bin/config.py
index 6e7d70b8..28241b42 100644
--- a/bin/config.py
+++ b/bin/config.py
@@ -129,6 +129,7 @@ def __init__(self, source: str | Path, **kwargs: Any) -> None:
 
         def warn(msg: Any) -> None:
             global n_warn
+            # `config` is imported before `util`, so we cannot use a `PrintBar` or `eprint` here.
             print(f"{Fore.YELLOW}WARNING: {msg}{Style.RESET_ALL}", file=sys.stderr)
             n_warn += 1
 
@@ -271,15 +272,12 @@ def get_arg(key: str, default: T, constraint: Optional[str] = None) -> T:
             print(key, type(kwargs[key]))
             warn(f"unknown key in {source}: '{key}'")
 
-    def update(self, args: "ARGS", replace: bool = False) -> None:
+    def add_if_not_set(self, args: "ARGS") -> None:
         for key in args._set:
-            if key not in self._set or replace:
+            if key not in self._set:
                 setattr(self, key, getattr(args, key))
                 self._set.add(key)
 
-    def mark_set(self, *keys: str) -> None:
-        self._set.update(list(keys))
-
     def copy(self) -> "ARGS":
         res = copy.copy(self)
         res._set = copy.copy(res._set)
diff --git a/bin/tools.py b/bin/tools.py
index 5fd62dba..3efe1504 100755
--- a/bin/tools.py
+++ b/bin/tools.py
@@ -1058,7 +1058,7 @@ def build_parser() -> SuppressingParser:
     return parser
 
 
-def find_personal_config() -> Optional[Path]:
+def find_home_config_dir() -> Optional[Path]:
     if is_windows():
         app_data = os.getenv("AppData")
         return Path(app_data) if app_data else None
@@ -1071,14 +1071,14 @@ def find_personal_config() -> Optional[Path]:
 
 
 def read_personal_config(problem_dir: Optional[Path]) -> None:
-    home_config = find_personal_config()
+    home_config_dir = find_home_config_dir()
     # possible config files, sorted by priority
     config_files = []
     if problem_dir:
         config_files.append(problem_dir / ".bapctools.yaml")
     config_files.append(Path.cwd() / ".bapctools.yaml")
-    if home_config:
-        config_files.append(home_config / "bapctools" / "config.yaml")
+    if home_config_dir:
+        config_files.append(home_config_dir / "bapctools" / "config.yaml")
 
     for config_file in config_files:
         if not config_file.is_file():
@@ -1091,8 +1091,7 @@ def read_personal_config(problem_dir: Optional[Path]) -> None:
             warn(f"invalid data in {config_data}. SKIPPED.")
             continue
 
-        tmp = config.ARGS(config_file, **config_data)
-        config.args.update(tmp)
+        config.args.add_if_not_set(config.ARGS(config_file, **config_data))
 
 
 def run_parsed_arguments(args: argparse.Namespace, personal_config: bool = True) -> None:
diff --git a/test/test_default_output_validator.py b/test/test_default_output_validator.py
index a904ad8c..ed47bdbe 100644
--- a/test/test_default_output_validator.py
+++ b/test/test_default_output_validator.py
@@ -15,9 +15,7 @@
 # Note: the python version isn't tested by default, because it's quite slow.
 DEFAULT_OUTPUT_VALIDATOR = ["default_output_validator.cpp"]
 
-config.args.verbose = 2
-config.args.error = True
-config.args.mark_set("verbose", "error")
+config.args.add_if_not_set(config.ARGS("test_default_output_validator.py", verbose=2, error=True))
 
 
 # return list of (flags, ans, out, expected result)
diff --git a/test/test_problem_yaml.py b/test/test_problem_yaml.py
index 8107d2ea..31da03e9 100644
--- a/test/test_problem_yaml.py
+++ b/test/test_problem_yaml.py
@@ -9,9 +9,7 @@
 
 RUN_DIR = Path.cwd().absolute()
 
-config.args.verbose = 2
-config.args.error = True
-config.args.mark_set("verbose", "error")
+config.args.add_if_not_set(config.ARGS("test_problem_yaml.py", verbose=2, error=True))
 
 
 # return list of {yaml: {...}, ...} documents