diff --git a/src/dbus_fast/auth.py b/src/dbus_fast/auth.py
index a4c4b37a..b7462d0f 100644
--- a/src/dbus_fast/auth.py
+++ b/src/dbus_fast/auth.py
@@ -4,6 +4,8 @@
 
 from .errors import AuthError
 
+UID_NOT_SPECIFIED = -1
+
 # The auth interface here is unstable. I would like to eventually open this up
 # for people to define their own custom authentication protocols, but I'm not
 # familiar with what's needed for that exactly. To work with any message bus
@@ -68,7 +70,7 @@ def __init__(self, uid: int = None) -> None:
     def _authentication_start(self, negotiate_unix_fd: bool = False) -> str:
         self.negotiate_unix_fd = negotiate_unix_fd
         uid = self.uid
-        if uid == -1:
+        if uid == UID_NOT_SPECIFIED:
             return "AUTH EXTERNAL"
         if uid is None:
             uid = os.getuid()
@@ -88,7 +90,7 @@ def _receive_line(self, line: str) -> str:
         if response is _AuthResponse.AGREE_UNIX_FD:
             return "BEGIN"
 
-        if response is _AuthResponse.DATA and self.uid == -1:
+        if response is _AuthResponse.DATA and self.uid == UID_NOT_SPECIFIED:
             return "DATA"
 
         raise AuthError(f"authentication failed: {response.value}: {args}")
diff --git a/tests/test_auth.py b/tests/test_auth.py
index 70019bce..47b25594 100644
--- a/tests/test_auth.py
+++ b/tests/test_auth.py
@@ -3,7 +3,7 @@
 
 import pytest
 
-from dbus_fast.auth import AuthExternal
+from dbus_fast.auth import AuthExternal, UID_NOT_SPECIFIED
 
 
 def test_uid_is_set():
@@ -12,6 +12,6 @@ def test_uid_is_set():
 
 
 def test_no_uid():
-    auth = AuthExternal(uid=-1)
+    auth = AuthExternal(uid=UID_NOT_SPECIFIED)
     assert auth._authentication_start() == "AUTH EXTERNAL"
     assert auth._receive_line("DATA") == "DATA"