diff --git a/stdlib/2and3/hmac.pyi b/stdlib/2and3/hmac.pyi
index bac39182b..5b2b705e4 100644
--- a/stdlib/2and3/hmac.pyi
+++ b/stdlib/2and3/hmac.pyi
@@ -5,8 +5,6 @@ from _typeshed import ReadableBuffer
 from types import ModuleType
 from typing import Any, AnyStr, Callable, Optional, Union, overload
 
-_B = Union[bytes, bytearray]
-
 # TODO more precise type for object of hashlib
 _Hash = Any
 _DigestMod = Union[str, Callable[[], _Hash], ModuleType]
@@ -17,15 +15,15 @@ if sys.version_info >= (3, 8):
     # In reality digestmod has a default value, but the function always throws an error
     # if the argument is not given, so we pretend it is a required argument.
     @overload
-    def new(key: _B, msg: Optional[ReadableBuffer], digestmod: _DigestMod) -> HMAC: ...
+    def new(key: bytes, msg: Optional[ReadableBuffer], digestmod: _DigestMod) -> HMAC: ...
     @overload
-    def new(key: _B, *, digestmod: _DigestMod) -> HMAC: ...
+    def new(key: bytes, *, digestmod: _DigestMod) -> HMAC: ...
 
 elif sys.version_info >= (3, 4):
-    def new(key: _B, msg: Optional[ReadableBuffer] = ..., digestmod: Optional[_DigestMod] = ...) -> HMAC: ...
+    def new(key: bytes, msg: Optional[ReadableBuffer] = ..., digestmod: Optional[_DigestMod] = ...) -> HMAC: ...
 
 else:
-    def new(key: _B, msg: Optional[ReadableBuffer] = ..., digestmod: Optional[_DigestMod] = ...) -> HMAC: ...
+    def new(key: bytes, msg: Optional[ReadableBuffer] = ..., digestmod: Optional[_DigestMod] = ...) -> HMAC: ...
 
 class HMAC:
     if sys.version_info >= (3,):
@@ -33,15 +31,16 @@ class HMAC:
     if sys.version_info >= (3, 4):
         block_size: int
         name: str
+    def __init__(self, key: bytes, msg: Optional[ReadableBuffer] = ..., digestmod: _DigestMod = ...) -> None: ...
     def update(self, msg: ReadableBuffer) -> None: ...
     def digest(self) -> bytes: ...
     def hexdigest(self) -> str: ...
     def copy(self) -> HMAC: ...
 
 @overload
-def compare_digest(a: ReadableBuffer, b: ReadableBuffer) -> bool: ...
+def compare_digest(__a: ReadableBuffer, __b: ReadableBuffer) -> bool: ...
 @overload
-def compare_digest(a: AnyStr, b: AnyStr) -> bool: ...
+def compare_digest(__a: AnyStr, __b: AnyStr) -> bool: ...
 
 if sys.version_info >= (3, 7):
-    def digest(key: _B, msg: ReadableBuffer, digest: str) -> bytes: ...
+    def digest(key: bytes, msg: ReadableBuffer, digest: str) -> bytes: ...