diff --git a/pytorch3d/implicitron/tools/config.py b/pytorch3d/implicitron/tools/config.py
index 2f0bc40e..6a64dbaa 100644
--- a/pytorch3d/implicitron/tools/config.py
+++ b/pytorch3d/implicitron/tools/config.py
@@ -783,16 +783,16 @@ def expand_args_fields(
     Similarly, replace,
 
         x: Optional[X]
+        x_enabled: bool = ...
 
     and optionally
 
         def create_x(self):...
-        x_enabled: bool = ...
 
     with
 
         x_args: dict = dataclasses.field(default_factory=lambda: get_default_args(X))
-        x_enabled: bool = False
+        x_enabled: bool = ...
         def create_x(self):
             self.create_x_impl(self.x_enabled, self.x_args)
 
@@ -1091,8 +1091,10 @@ def _process_member(
         if process_type == _ProcessType.OPTIONAL_CONFIGURABLE:
             enabled_name = name + ENABLED_SUFFIX
             if enabled_name not in some_class.__annotations__:
-                some_class.__annotations__[enabled_name] = bool
-                setattr(some_class, enabled_name, False)
+                raise ValueError(
+                    f"{name} is an Optional[{type_.__name__}] member "
+                    f"but there is no corresponding member {enabled_name}."
+                )
 
     creation_function_name = f"{CREATE_PREFIX}{name}"
     if not hasattr(some_class, creation_function_name):
diff --git a/tests/implicitron/test_config.py b/tests/implicitron/test_config.py
index e86d12aa..e5ddec37 100644
--- a/tests/implicitron/test_config.py
+++ b/tests/implicitron/test_config.py
@@ -446,6 +446,7 @@ class TestConfig(unittest.TestCase):
             b2: Optional[B]
             b3: Optional[B]
             b2_enabled: bool = True
+            b3_enabled: bool = False
 
             def __post_init__(self):
                 run_auto_creation(self)
@@ -681,9 +682,10 @@ class TestConfig(unittest.TestCase):
     def test_remove_unused_components_optional(self):
         class MainTestWrapper(Configurable):
             mt: Optional[MainTest]
+            mt_enabled: bool = False
 
         args = get_default_args(MainTestWrapper)
-        self.assertEqual(list(args.keys()), ["mt_args", "mt_enabled"])
+        self.assertEqual(list(args.keys()), ["mt_enabled", "mt_args"])
         remove_unused_components(args)
         self.assertEqual(OmegaConf.to_yaml(args), "mt_enabled: false\n")
 
@@ -775,6 +777,7 @@ class TestConfig(unittest.TestCase):
                 boring_o: Optional[BoringConfigurable]
                 boring_o_enabled: bool = True
                 boring_0: Optional[BoringConfigurable]
+                boring_0_enabled: bool = False
 
                 def __post_init__(self):
                     run_auto_creation(self)