diff --git a/Lib/os.py b/Lib/os.py
index ea09e8c7e10489..d26cfc99939f39 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -983,16 +983,16 @@ def popen(cmd, mode="r", buffering=-1):
         import subprocess, io
         if mode == "r":
             proc = subprocess.Popen(cmd,
-                                    shell=True,
+                                    shell=True, text=True,
                                     stdout=subprocess.PIPE,
                                     bufsize=buffering)
-            return _wrap_close(io.TextIOWrapper(proc.stdout), proc)
+            return _wrap_close(proc.stdout, proc)
         else:
             proc = subprocess.Popen(cmd,
-                                    shell=True,
+                                    shell=True, text=True,
                                     stdin=subprocess.PIPE,
                                     bufsize=buffering)
-            return _wrap_close(io.TextIOWrapper(proc.stdin), proc)
+            return _wrap_close(proc.stdin, proc)
 
     # Helper for popen() -- a proxy for a file whose close waits for the process
     class _wrap_close:
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 96fddc7d057663..8b3d1feb78fe36 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -269,7 +269,7 @@ def test_write_windows_console(self):
 
     def fdopen_helper(self, *args):
         fd = os.open(os_helper.TESTFN, os.O_RDONLY)
-        f = os.fdopen(fd, *args)
+        f = os.fdopen(fd, *args, encoding="utf-8")
         f.close()
 
     def test_fdopen(self):
@@ -290,7 +290,7 @@ def test_replace(self):
 
         os.replace(os_helper.TESTFN, TESTFN2)
         self.assertRaises(FileNotFoundError, os.stat, os_helper.TESTFN)
-        with open(TESTFN2, 'r') as f:
+        with open(TESTFN2, 'r', encoding='utf-8') as f:
             self.assertEqual(f.read(), "1")
 
     def test_open_keywords(self):
@@ -1627,7 +1627,7 @@ def test_exist_ok_s_isgid_directory(self):
     def test_exist_ok_existing_regular_file(self):
         base = os_helper.TESTFN
         path = os.path.join(os_helper.TESTFN, 'dir1')
-        with open(path, 'w') as f:
+        with open(path, 'w', encoding='utf-8') as f:
             f.write('abc')
         self.assertRaises(OSError, os.makedirs, path)
         self.assertRaises(OSError, os.makedirs, path, exist_ok=False)
@@ -2094,7 +2094,7 @@ def test_chmod(self):
 
 
 class TestInvalidFD(unittest.TestCase):
-    singles = ["fchdir", "dup", "fdopen", "fdatasync", "fstat",
+    singles = ["fchdir", "dup", "fdatasync", "fstat",
                "fstatvfs", "fsync", "tcgetpgrp", "ttyname"]
     #singles.append("close")
     #We omit close because it doesn't raise an exception on some platforms
@@ -2106,15 +2106,18 @@ def helper(self):
     for f in singles:
         locals()["test_"+f] = get_single(f)
 
-    def check(self, f, *args):
+    def check(self, f, *args, **kwargs):
         try:
-            f(os_helper.make_bad_fd(), *args)
+            f(os_helper.make_bad_fd(), *args, **kwargs)
         except OSError as e:
             self.assertEqual(e.errno, errno.EBADF)
         else:
             self.fail("%r didn't raise an OSError with a bad file descriptor"
                       % f)
 
+    def test_fdopen(self):
+        self.check(os.fdopen, encoding="utf-8")
+
     @unittest.skipUnless(hasattr(os, 'isatty'), 'test needs os.isatty()')
     def test_isatty(self):
         self.assertEqual(os.isatty(os_helper.make_bad_fd()), False)
@@ -2210,7 +2213,7 @@ def _test_link(self, file1, file2):
             os.link(file1, file2)
         except PermissionError as e:
             self.skipTest('os.link(): %s' % e)
-        with open(file1, "r") as f1, open(file2, "r") as f2:
+        with open(file1, "rb") as f1, open(file2, "rb") as f2:
             self.assertTrue(os.path.sameopenfile(f1.fileno(), f2.fileno()))
 
     def test_link(self):
@@ -3009,7 +3012,7 @@ def create_args(self, *, with_env=False, use_bytes=False):
             code = ('import sys, os; magic = os.environ[%r]; sys.exit(%s)'
                     % (self.key, self.exitcode))
 
-        with open(filename, "w") as fp:
+        with open(filename, "w", encoding="utf-8") as fp:
             fp.write(code)
 
         args = [sys.executable, filename]
@@ -3149,7 +3152,7 @@ def _test_invalid_env(self, spawn):
         # equal character in the environment variable value
         filename = os_helper.TESTFN
         self.addCleanup(os_helper.unlink, filename)
-        with open(filename, "w") as fp:
+        with open(filename, "w", encoding="utf-8") as fp:
             fp.write('import sys, os\n'
                      'if os.getenv("FRUIT") != "orange=lemon":\n'
                      '    raise AssertionError')