diff --git a/chanfig/nested_dict.py b/chanfig/nested_dict.py
index 66bceca1..f68c4ac3 100644
--- a/chanfig/nested_dict.py
+++ b/chanfig/nested_dict.py
@@ -155,14 +155,16 @@ def __init__(
         self,
         *args: Any,
         default_factory: Callable | None = None,
-        convert_mapping: bool = False,
-        fallback: bool = False,
+        convert_mapping: bool | None = None,
+        fallback: bool | None = None,
         **kwargs: Any,
     ) -> None:
         super().__init__(default_factory)
         self.merge(*args, **kwargs)
-        self.setattr("convert_mapping", convert_mapping)
-        self.setattr("fallback", fallback)
+        if convert_mapping is not None:
+            self.setattr("convert_mapping", convert_mapping)
+        if fallback is not None:
+            self.setattr("fallback", fallback)
 
     def all_keys(self) -> Generator:
         r"""
diff --git a/chanfig/registry.py b/chanfig/registry.py
index e912e331..c630fd2b 100644
--- a/chanfig/registry.py
+++ b/chanfig/registry.py
@@ -88,9 +88,10 @@ class Registry(NestedDict):  # type: ignore
 
     override: bool = False
 
-    def __init__(self, override: bool = False, fallback: bool = False):
+    def __init__(self, override: bool | None = None, fallback: bool | None = None):
         super().__init__(fallback=fallback)
-        self.setattr("override", override)
+        if override is not None:
+            self.setattr("override", override)
 
     def register(self, component: Any = None, name: Any | None = None) -> Callable:
         r"""