diff --git a/hgext/phabricator.py b/hgext/phabricator.py
--- a/hgext/phabricator.py
+++ b/hgext/phabricator.py
@@ -62,6 +62,7 @@ from __future__ import absolute_import
 import base64
 import contextlib
 import hashlib
+import io
 import itertools
 import json
 import mimetypes
@@ -2200,7 +2201,7 @@ def phabimport(ui, repo, *specs, **opts)
             for drev, contents in patches:
                 ui.status(_(b'applying patch from D%s\n') % drev)
 
-                with patch.extract(ui, pycompat.bytesio(contents)) as patchdata:
+                with patch.extract(ui, io.BytesIO(contents)) as patchdata:
                     msg, node, rej = cmdutil.tryimportone(
                         ui,
                         repo,
diff --git a/mercurial/pure/mpatch.py b/mercurial/pure/mpatch.py
--- a/mercurial/pure/mpatch.py
+++ b/mercurial/pure/mpatch.py
@@ -7,11 +7,11 @@
 
 from __future__ import absolute_import
 
+import io
 import struct
 
-from .. import pycompat
 
-stringio = pycompat.bytesio
+stringio = io.BytesIO
 
 
 class mpatchError(Exception):
diff --git a/mercurial/pure/parsers.py b/mercurial/pure/parsers.py
--- a/mercurial/pure/parsers.py
+++ b/mercurial/pure/parsers.py
@@ -7,6 +7,7 @@
 
 from __future__ import absolute_import
 
+import io
 import stat
 import struct
 import zlib
@@ -26,7 +27,7 @@ from .. import (
 from ..revlogutils import nodemap as nodemaputil
 from ..revlogutils import constants as revlog_constants
 
-stringio = pycompat.bytesio
+stringio = io.BytesIO
 
 
 _pack = struct.pack
diff --git a/mercurial/pycompat.py b/mercurial/pycompat.py
--- a/mercurial/pycompat.py
+++ b/mercurial/pycompat.py
@@ -111,9 +111,6 @@ sysplatform = sys.platform.encode('ascii
 sysexecutable = sys.executable
 if sysexecutable:
     sysexecutable = os.fsencode(sysexecutable)
-bytesio = io.BytesIO
-# TODO deprecate stringio name, as it is a lie on Python 3.
-stringio = bytesio
 
 
 def maplist(*args):
diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -21,6 +21,7 @@ import contextlib
 import errno
 import gc
 import hashlib
+import io
 import itertools
 import locale
 import mmap
@@ -78,7 +79,7 @@ cookielib = pycompat.cookielib
 httplib = pycompat.httplib
 safehasattr = pycompat.safehasattr
 socketserver = pycompat.socketserver
-bytesio = pycompat.bytesio
+bytesio = io.BytesIO
 # TODO deprecate stringio name, as it is a lie on Python 3.
 stringio = bytesio
 xmlrpclib = pycompat.xmlrpclib
diff --git a/tests/test-basic.t b/tests/test-basic.t
--- a/tests/test-basic.t
+++ b/tests/test-basic.t
@@ -240,15 +240,16 @@ Invalid ui.message-output option:
 Underlying message streams should be updated when ui.fout/ferr are set:
 
   $ cat <<'EOF' > capui.py
-  > from mercurial import pycompat, registrar
+  > import io
+  > from mercurial import registrar
   > cmdtable = {}
   > command = registrar.command(cmdtable)
   > @command(b'capui', norepo=True)
   > def capui(ui):
   >     out = ui.fout
-  >     ui.fout = pycompat.bytesio()
+  >     ui.fout = io.BytesIO()
   >     ui.status(b'status\n')
-  >     ui.ferr = pycompat.bytesio()
+  >     ui.ferr = io.BytesIO()
   >     ui.warn(b'warn\n')
   >     out.write(b'stdout: %s' % ui.fout.getvalue())
   >     out.write(b'stderr: %s' % ui.ferr.getvalue())
diff --git a/tests/test-util.py b/tests/test-util.py
--- a/tests/test-util.py
+++ b/tests/test-util.py
@@ -2,6 +2,7 @@
 from __future__ import absolute_import
 
 import contextlib
+import io
 import itertools
 import unittest
 
@@ -55,7 +56,7 @@ def mocktimer(incr=0.1, *additional_targ
 
 @contextlib.contextmanager
 def capturestderr():
-    """Replace utils.procutil.stderr with a pycompat.bytesio instance
+    """Replace utils.procutil.stderr with an io.BytesIO instance
 
     The instance is made available as the return value of __enter__.
 
@@ -63,7 +64,7 @@ def capturestderr():
 
     """
     orig = utils.procutil.stderr
-    utils.procutil.stderr = pycompat.bytesio()
+    utils.procutil.stderr = io.BytesIO()
     try:
         yield utils.procutil.stderr
     finally: