diff --git a/src/dbus_fast/auth.py b/src/dbus_fast/auth.py
index c491980..09fa6f6 100644
--- a/src/dbus_fast/auth.py
+++ b/src/dbus_fast/auth.py
@@ -1,5 +1,6 @@
 import enum
 import os
+from typing import List, Tuple
 
 from .errors import AuthError
 
@@ -11,7 +12,7 @@ from .errors import AuthError
 # doing that. I might just end up giving the raw socket and leaving it all up
 # to the user, but it would be nice to have a little guidance in the interface
 # since a lot of it is strongly specified. If you have a need for this, contact
-# the project maintainer to help stabalize this interface.
+# the project maintainer to help stabilize this interface.
 
 
 class _AuthResponse(enum.Enum):
@@ -22,7 +23,7 @@ class _AuthResponse(enum.Enum):
     AGREE_UNIX_FD = "AGREE_UNIX_FD"
 
     @classmethod
-    def parse(klass, line):
+    def parse(klass, line: str) -> Tuple["_AuthResponse", List[str]]:
         args = line.split(" ")
         response = klass(args[0])
         return response, args[1:]
@@ -37,18 +38,18 @@ class Authenticator:
     :seealso: https://dbus.freedesktop.org/doc/dbus-specification.html#auth-protocol
     """
 
-    def _authentication_start(self, negotiate_unix_fd=False):
+    def _authentication_start(self, negotiate_unix_fd: bool = False) -> str:
         raise NotImplementedError(
             "authentication_start() must be implemented in the inheriting class"
         )
 
-    def _receive_line(self, line):
+    def _receive_line(self, line: str) -> str:
         raise NotImplementedError(
             "receive_line() must be implemented in the inheriting class"
         )
 
     @staticmethod
-    def _format_line(line):
+    def _format_line(line: str) -> bytes:
         return f"{line}\r\n".encode()
 
 
@@ -59,16 +60,16 @@ class AuthExternal(Authenticator):
     :sealso: https://dbus.freedesktop.org/doc/dbus-specification.html#auth-protocol
     """
 
-    def __init__(self):
-        self.negotiate_unix_fd = False
-        self.negotiating_fds = False
+    def __init__(self) -> None:
+        self.negotiate_unix_fd: bool = False
+        self.negotiating_fds: bool = False
 
-    def _authentication_start(self, negotiate_unix_fd=False) -> str:
+    def _authentication_start(self, negotiate_unix_fd: bool = False) -> str:
         self.negotiate_unix_fd = negotiate_unix_fd
         hex_uid = str(os.getuid()).encode().hex()
         return f"AUTH EXTERNAL {hex_uid}"
 
-    def _receive_line(self, line: str):
+    def _receive_line(self, line: str) -> str:
         response, args = _AuthResponse.parse(line)
 
         if response is _AuthResponse.OK:
@@ -91,7 +92,7 @@ class AuthAnnonymous(Authenticator):
     :sealso: https://dbus.freedesktop.org/doc/dbus-specification.html#auth-protocol
     """
 
-    def _authentication_start(self, negotiate_unix_fd=False) -> str:
+    def _authentication_start(self, negotiate_unix_fd: bool = False) -> str:
         if negotiate_unix_fd:
             raise AuthError(
                 "annonymous authentication does not support negotiating unix fds right now"