diff --git a/redbot/core/config.py b/redbot/core/config.py
index dc6bbed7464..3b3f921d032 100644
--- a/redbot/core/config.py
+++ b/redbot/core/config.py
@@ -141,6 +141,9 @@ class Value:
 
     """
 
+    # to reserve these attributes for __getattr__
+    __slots__ = ("identifier_data", "default", "_driver", "_config", "__dict__")
+
     def __init__(self, identifier_data: IdentifierData, default_value, driver, config: "Config"):
         self.identifier_data = identifier_data
         self.default = default_value
@@ -291,6 +294,9 @@ class Group(Value):
 
     """
 
+    # to reserve these attributes for __getattr__
+    __slots__ = ("_defaults", "force_registration")
+
     def __init__(
         self,
         identifier_data: IdentifierData,
@@ -640,6 +646,19 @@ class Config(metaclass=ConfigMeta):
     USER = "USER"
     MEMBER = "MEMBER"
 
+    # to reserve these attributes for __getattr__
+    __slots__ = (
+        "cog_name",
+        "unique_identifier",
+        "_driver",
+        "force_registration",
+        "_defaults",
+        "custom_groups",
+        "_lock_cache",
+        "__weakref__",
+        "__dict__",
+    )
+
     def __init__(
         self,
         cog_name: str,
@@ -782,6 +801,8 @@ def _get_defaults_dict(key: str, value) -> dict:
         for i, k in enumerate(splitted, start=1):
             if not k.isidentifier():
                 raise RuntimeError("'{}' is an invalid config key.".format(k))
+            if k in [*dir(Config), *dir(Group), *dir(Value)]:
+                raise RuntimeError("'{}' is a reserved config key.".format(k))
             if i == len(splitted):
                 partial[k] = value
             else:
diff --git a/tests/core/test_config.py b/tests/core/test_config.py
index ac34ae6885b..f3861354dba 100644
--- a/tests/core/test_config.py
+++ b/tests/core/test_config.py
@@ -16,6 +16,13 @@ def test_config_register_global_badvalues(config):
         config.register_global(**{"invalid var name": True})
 
 
+def test_config_register_reserved_keys(config):
+    config.register_global(**{"group": {"value": True}, "value": True})
+    for attr in [*dir(config), *dir(config.group), *dir(config.value)]:
+        with pytest.raises(RuntimeError):
+            config.register_global(**{attr: True})
+
+
 async def test_config_register_guild(config, empty_guild):
     config.register_guild(enabled=False, some_list=[], some_dict={})
     assert config.defaults[config.GUILD]["enabled"] is False