diff --git a/HISTORY.rst b/HISTORY.rst
index 53dc91c..49f7465 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -4,6 +4,7 @@ History
 FUTURE: TBD
 -----------
 - Update HISTORY.rst to reflect previous releases made on GitHub
+- Use SPNEGO mechanism by default
 
 0.4.0: 2024-11-28
 -----------------
diff --git a/README.rst b/README.rst
index a79aceb..c77cc02 100644
--- a/README.rst
+++ b/README.rst
@@ -171,10 +171,11 @@ applicable). However, an explicit credential can be in instead, if desired.
 Explicit Mechanism
 ------------------
 
-``HTTPSPNEGOAuth`` normally lets the underlying ``gssapi`` library decide which
-negotiation mechanism to use. However, an explicit mechanism can be used instead
-if desired. The ``mech`` parameter will be passed straight through to ``gssapi``
-without interference. It is expected to be an instance of ``gssapi.mechs.Mechanism``.
+``HTTPSPNEGOAuth`` normally lets SPNEGO decide which negotiation mechanism to use.
+However, an explicit mechanism can be used instead if desired. The ``mech``
+parameter will be passed straight through to ``gssapi`` without interference.
+It is expected to be an instance of ``gssapi.Mechanism``, ``gssapi.OID``, or
+raw bytes.
 
 .. code-block:: python
 
@@ -182,10 +183,10 @@ without interference. It is expected to be an instance of ``gssapi.mechs.Mechani
     >>> import httpx
     >>> from httpx_gssapi import HTTPSPNEGOAuth
     >>> try:
-    ...   spnego = gssapi,mechs.Mechanism.from_sasl_name("SPNEGO")
+    ...   krb5 = gssapi.mechs.Mechanism.from_sasl_name("GS2-KRB5")
     ... except AttributeError:
-    ...   spnego = gssapi.OID.from_int_seq("1.3.6.1.5.5.2")
-    >>> gssapi_auth = HTTPSPNEGOAuth(mech=spnego)
+    ...   krb5 = gssapi.OID.from_int_seq("1.2.840.113554.1.2.2")
+    >>> gssapi_auth = HTTPSPNEGOAuth(mech=krb5)
     >>> r = httpx.get("http://example.org", auth=gssapi_auth)
     ...
 
diff --git a/httpx_gssapi/__init__.py b/httpx_gssapi/__init__.py
index 7e8a994..3c53224 100644
--- a/httpx_gssapi/__init__.py
+++ b/httpx_gssapi/__init__.py
@@ -16,6 +16,7 @@
 __all__ = (
     'HTTPSPNEGOAuth',
     'MutualAuthenticationError',
+    'SPNEGO',
     'REQUIRED',
     'OPTIONAL',
     'DISABLED',
@@ -24,7 +25,7 @@
 import os
 import logging
 
-from .gssapi_ import HTTPSPNEGOAuth, REQUIRED, OPTIONAL, DISABLED
+from .gssapi_ import HTTPSPNEGOAuth, SPNEGO, REQUIRED, OPTIONAL, DISABLED
 from .exceptions import MutualAuthenticationError
 
 from ._version import get_versions
diff --git a/httpx_gssapi/gssapi_.py b/httpx_gssapi/gssapi_.py
index cdd613b..fcee28a 100644
--- a/httpx_gssapi/gssapi_.py
+++ b/httpx_gssapi/gssapi_.py
@@ -2,7 +2,7 @@
 import logging
 from itertools import chain
 from functools import wraps
-from typing import Generator, Optional, List, Any
+from typing import Generator, Optional, List, Any, Union
 
 from base64 import b64encode, b64decode
 
@@ -33,6 +33,9 @@
 OPTIONAL = 2
 DISABLED = 3
 
+# OID for the SPNEGO mechanism
+SPNEGO = gssapi.OID.from_int_seq("1.3.6.1.5.5.2")
+
 _find_auth = re.compile(r'Negotiate\s*([^,]*)', re.I).search
 
 
@@ -125,7 +128,9 @@ class HTTPSPNEGOAuth(Auth):
     Default is `None`.
 
     `mech` is GSSAPI Mechanism (gssapi.Mechanism) to use for negotiation.
-    Default is `None`
+    If explicitly given as ``None``, the underlying ``gssapi`` library will
+    decide which negotiation mechanism to use.
+    Default is `SPNEGO`.
 
     `sanitize_mutual_error_response` controls whether we should clean up
     server responses.  See the `SanitizedResponse` class.
@@ -138,7 +143,7 @@ def __init__(self,
                  delegate: bool = False,
                  opportunistic_auth: bool = False,
                  creds: gssapi.Credentials = None,
-                 mech: bytes = None,
+                 mech: Optional[Union[bytes, gssapi.OID]] = SPNEGO,
                  sanitize_mutual_error_response: bool = True):
         self.mutual_authentication = mutual_authentication
         self.target_name = target_name
diff --git a/tests/test_mocked.py b/tests/test_mocked.py
index 798a5b6..770bfc3 100644
--- a/tests/test_mocked.py
+++ b/tests/test_mocked.py
@@ -82,7 +82,7 @@ def null_response(status=200, request=null_request(), **kwargs):
 def check_init(**kwargs):
     kwargs.setdefault('name', gssapi_name("HTTP@www.example.org"))
     kwargs.setdefault('creds', None)
-    kwargs.setdefault('mech', None)
+    kwargs.setdefault('mech', gssapi.OID.from_int_seq("1.3.6.1.5.5.2"))
     kwargs.setdefault('flags', gssflags)
     kwargs.setdefault('usage', "initiate")
     fake_init.assert_called_with(**kwargs)
@@ -397,5 +397,14 @@ def test_target_name(patched_ctx):
     fake_resp.assert_called_with(b"token")
 
 
+def test_os_default_mech(patched_ctx):
+    resp = null_response(headers=neg_token)
+    auth = httpx_gssapi.HTTPSPNEGOAuth(mech=None)
+    auth.set_auth_header(resp.request, resp)
+    assert resp.request.headers['Authorization'] == b64_negotiate_response
+    check_init(mech=None)
+    fake_resp.assert_called_with(b"token")
+
+
 if __name__ == '__main__':
     pytest.main()