diff --git a/stdlib/binascii.pyi b/stdlib/binascii.pyi
index 317bb9979b92..53f72ad6a88f 100644
--- a/stdlib/binascii.pyi
+++ b/stdlib/binascii.pyi
@@ -1,36 +1,44 @@
 import sys
+from _typeshed import ReadableBuffer
+from typing_extensions import TypeAlias
 
-def a2b_uu(__data: str | bytes) -> bytes: ...
+# Many functions in binascii accept buffer objects
+# or ASCII-only strings.
+_AsciiBuffer: TypeAlias = str | ReadableBuffer
+
+def a2b_uu(__data: _AsciiBuffer) -> bytes: ...
 
 if sys.version_info >= (3, 7):
-    def b2a_uu(__data: bytes, *, backtick: bool = ...) -> bytes: ...
+    def b2a_uu(__data: ReadableBuffer, *, backtick: bool = ...) -> bytes: ...
 
 else:
-    def b2a_uu(__data: bytes) -> bytes: ...
+    def b2a_uu(__data: ReadableBuffer) -> bytes: ...
 
-def a2b_base64(__data: str | bytes) -> bytes: ...
-def b2a_base64(__data: bytes, *, newline: bool = ...) -> bytes: ...
-def a2b_qp(data: str | bytes, header: bool = ...) -> bytes: ...
-def b2a_qp(data: bytes, quotetabs: bool = ..., istext: bool = ..., header: bool = ...) -> bytes: ...
+def a2b_base64(__data: _AsciiBuffer) -> bytes: ...
+def b2a_base64(__data: ReadableBuffer, *, newline: bool = ...) -> bytes: ...
+def a2b_qp(data: _AsciiBuffer, header: bool = ...) -> bytes: ...
+def b2a_qp(data: ReadableBuffer, quotetabs: bool = ..., istext: bool = ..., header: bool = ...) -> bytes: ...
 
 if sys.version_info < (3, 11):
-    def a2b_hqx(__data: str | bytes) -> bytes: ...
-    def rledecode_hqx(__data: bytes) -> bytes: ...
-    def rlecode_hqx(__data: bytes) -> bytes: ...
-    def b2a_hqx(__data: bytes) -> bytes: ...
+    def a2b_hqx(__data: _AsciiBuffer) -> bytes: ...
+    def rledecode_hqx(__data: ReadableBuffer) -> bytes: ...
+    def rlecode_hqx(__data: ReadableBuffer) -> bytes: ...
+    def b2a_hqx(__data: ReadableBuffer) -> bytes: ...
 
-def crc_hqx(__data: bytes, __crc: int) -> int: ...
-def crc32(__data: bytes, __crc: int = ...) -> int: ...
-def b2a_hex(__data: bytes) -> bytes: ...
+def crc_hqx(__data: ReadableBuffer, __crc: int) -> int: ...
+def crc32(__data: ReadableBuffer, __crc: int = ...) -> int: ...
 
 if sys.version_info >= (3, 8):
-    def hexlify(data: bytes, sep: str | bytes = ..., bytes_per_sep: int = ...) -> bytes: ...
+    # sep must be str or bytes, not bytearray or any other buffer
+    def b2a_hex(data: ReadableBuffer, sep: str | bytes = ..., bytes_per_sep: int = ...) -> bytes: ...
+    def hexlify(data: ReadableBuffer, sep: str | bytes = ..., bytes_per_sep: int = ...) -> bytes: ...
 
 else:
-    def hexlify(__data: bytes) -> bytes: ...
+    def b2a_hex(__data: ReadableBuffer) -> bytes: ...
+    def hexlify(__data: ReadableBuffer) -> bytes: ...
 
-def a2b_hex(__hexstr: str | bytes) -> bytes: ...
-def unhexlify(__hexstr: str | bytes) -> bytes: ...
+def a2b_hex(__hexstr: _AsciiBuffer) -> bytes: ...
+def unhexlify(__hexstr: _AsciiBuffer) -> bytes: ...
 
 class Error(ValueError): ...
 class Incomplete(Exception): ...