diff --git a/.flake8 b/.flake8
index abbd0dc..10c3960 100644
--- a/.flake8
+++ b/.flake8
@@ -1,3 +1,3 @@
 [flake8]
 max-line-length = 88
-ignore = E203, W503
+extend-ignore = E203,W503,E701
diff --git a/fido2/client.py b/fido2/client.py
index 3185871..860f908 100644
--- a/fido2/client.py
+++ b/fido2/client.py
@@ -68,6 +68,7 @@
     Mapping,
     Sequence,
     Tuple,
+    overload,
 )
 
 import abc
@@ -463,6 +464,14 @@ def _get_extension_results(self, assertion):
         return ClientExtensionOutputs(extension_outputs)
 
 
+@overload
+def _cbor_list(values: Sequence) -> list: ...
+
+
+@overload
+def _cbor_list(values: None) -> None: ...
+
+
 def _cbor_list(values):
     if not values:
         return None
diff --git a/fido2/ctap2/base.py b/fido2/ctap2/base.py
index 4fd1390..29a041c 100644
--- a/fido2/ctap2/base.py
+++ b/fido2/ctap2/base.py
@@ -135,7 +135,7 @@ class AssertionResponse(_CborDataObject):
         (only set for the first response, if > 1).
     """
 
-    credential: Dict[str, Any]
+    credential: Mapping[str, Any]
     auth_data: AuthenticatorData
     signature: bytes
     user: Optional[Dict[str, Any]] = None
@@ -154,7 +154,7 @@ def verify(self, client_param: bytes, public_key: CoseKey):
 
     @classmethod
     def from_ctap1(
-        cls, app_param: bytes, credential: Dict[str, Any], authentication
+        cls, app_param: bytes, credential: Mapping[str, Any], authentication
     ) -> "AssertionResponse":
         """Create an AssertionResponse from a CTAP1 SignatureData instance.
 
diff --git a/fido2/utils.py b/fido2/utils.py
index 34be309..df80e20 100644
--- a/fido2/utils.py
+++ b/fido2/utils.py
@@ -48,6 +48,8 @@
     TypeVar,
     Hashable,
     get_type_hints,
+    overload,
+    Type,
 )
 import struct
 import warnings
@@ -168,6 +170,7 @@ def read(self, size: Optional[int] = -1) -> bytes:
 
 
 _T = TypeVar("_T", bound=Hashable)
+_S = TypeVar("_S", bound="_DataClassMapping")
 
 
 class _DataClassMapping(Mapping[_T, Any]):
@@ -252,8 +255,16 @@ def _parse_value(cls, t, value):
         # Convert to enum values, other wrappers
         return t(value)
 
+    @overload
     @classmethod
-    def from_dict(cls, data: Optional[Mapping[_T, Any]]):
+    def from_dict(cls: Type[_S], data: None) -> None: ...
+
+    @overload
+    @classmethod
+    def from_dict(cls: Type[_S], data: Mapping[_T, Any]) -> _S: ...
+
+    @classmethod
+    def from_dict(cls, data):
         if data is None:
             return None
         if isinstance(data, cls):
diff --git a/fido2/webauthn.py b/fido2/webauthn.py
index ba7a6fc..33e7a72 100644
--- a/fido2/webauthn.py
+++ b/fido2/webauthn.py
@@ -464,7 +464,7 @@ def _parse_value(cls, t, value):
         return super(_JsonDataObject, cls)._parse_value(t, value)
 
     @classmethod
-    def from_dict(cls, data: Optional[Mapping[str, Any]]):
+    def from_dict(cls, data):
         webauthn_json_mapping.warn()
         return super().from_dict(data)
 
@@ -566,7 +566,7 @@ def __getitem__(self, key):
         return super().__getitem__(key)
 
     @classmethod
-    def from_dict(cls, data: Optional[Mapping[str, Any]]):
+    def from_dict(cls, data):
         if data is not None and not webauthn_json_mapping.enabled:
             value = dict(data)
             value["clientDataJSON"] = value.pop("clientData", None)
@@ -596,7 +596,7 @@ def __getitem__(self, key):
         return super().__getitem__(key)
 
     @classmethod
-    def from_dict(cls, data: Optional[Mapping[str, Any]]):
+    def from_dict(cls, data):
         if data is not None and not webauthn_json_mapping.enabled:
             value = dict(data)
             value["clientDataJSON"] = value.pop("clientData", None)