diff --git a/mercurial/__init__.py b/mercurial/__init__.py
--- a/mercurial/__init__.py
+++ b/mercurial/__init__.py
@@ -31,9 +31,6 @@ if sys.version_info[0] >= 3:
             # Only handle Mercurial-related modules.
             if not fullname.startswith(('mercurial.', 'hgext.', 'hgext3rd.')):
                 return None
-            # selectors2 is already dual-version clean, don't try and mangle it
-            if fullname.startswith('mercurial.selectors2'):
-                return None
             # third-party packages are expected to be dual-version clean
             if fullname.startswith('mercurial.thirdparty'):
                 return None
diff --git a/mercurial/commandserver.py b/mercurial/commandserver.py
--- a/mercurial/commandserver.py
+++ b/mercurial/commandserver.py
@@ -17,11 +17,11 @@ import struct
 import traceback
 
 from .i18n import _
+from .thirdparty import selectors2
 from . import (
     encoding,
     error,
     pycompat,
-    selectors2,
     util,
 )
 
diff --git a/mercurial/selectors2.py b/mercurial/thirdparty/selectors2.py
rename from mercurial/selectors2.py
rename to mercurial/thirdparty/selectors2.py
--- a/mercurial/selectors2.py
+++ b/mercurial/thirdparty/selectors2.py
@@ -22,8 +22,6 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
-# no-check-code
-
 from __future__ import absolute_import
 
 import collections
@@ -34,7 +32,7 @@ import socket
 import sys
 import time
 
-from . import pycompat
+from .. import pycompat
 
 namedtuple = collections.namedtuple
 Mapping = collections.Mapping
diff --git a/tests/test-check-code.t b/tests/test-check-code.t
--- a/tests/test-check-code.t
+++ b/tests/test-check-code.t
@@ -15,7 +15,6 @@ New errors are not allowed. Warnings are
   Skipping i18n/polib.py it has no-che?k-code (glob)
   Skipping mercurial/httpclient/__init__.py it has no-che?k-code (glob)
   Skipping mercurial/httpclient/_readers.py it has no-che?k-code (glob)
-  Skipping mercurial/selectors2.py it has no-che?k-code (glob)
   Skipping mercurial/statprof.py it has no-che?k-code (glob)
   Skipping tests/badserverext.py it has no-che?k-code (glob)