diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index c731302..d493b19 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -407,10 +407,12 @@ def large_file_ops(self, f):
     def test_invalid_operations(self):
         # Try writing on a file opened in read mode and vice-versa.
         exc = self.UnsupportedOperation
-        for mode in ("w", "wb"):
-            with self.open(os_helper.TESTFN, mode) as fp:
-                self.assertRaises(exc, fp.read)
-                self.assertRaises(exc, fp.readline)
+        with self.open(os_helper.TESTFN, "w", encoding="utf-8") as fp:
+            self.assertRaises(exc, fp.read)
+            self.assertRaises(exc, fp.readline)
+        with self.open(os_helper.TESTFN, "wb") as fp:
+            self.assertRaises(exc, fp.read)
+            self.assertRaises(exc, fp.readline)
         with self.open(os_helper.TESTFN, "wb", buffering=0) as fp:
             self.assertRaises(exc, fp.read)
             self.assertRaises(exc, fp.readline)
@@ -420,7 +422,7 @@ def test_invalid_operations(self):
         with self.open(os_helper.TESTFN, "rb") as fp:
             self.assertRaises(exc, fp.write, b"blah")
             self.assertRaises(exc, fp.writelines, [b"blah\n"])
-        with self.open(os_helper.TESTFN, "r") as fp:
+        with self.open(os_helper.TESTFN, "r", encoding="utf-8") as fp:
             self.assertRaises(exc, fp.write, "blah")
             self.assertRaises(exc, fp.writelines, ["blah\n"])
             # Non-zero seeking from current or end pos
@@ -533,12 +535,12 @@ class UnseekableWriter(self.MockUnseekableIO):
 
     def test_open_handles_NUL_chars(self):
         fn_with_NUL = 'foo\0bar'
-        self.assertRaises(ValueError, self.open, fn_with_NUL, 'w')
+        self.assertRaises(ValueError, self.open, fn_with_NUL, 'w', encoding="utf-8")
 
         bytes_fn = bytes(fn_with_NUL, 'ascii')
         with warnings.catch_warnings():
             warnings.simplefilter("ignore", DeprecationWarning)
-            self.assertRaises(ValueError, self.open, bytes_fn, 'w')
+            self.assertRaises(ValueError, self.open, bytes_fn, 'w', encoding="utf-8")
 
     def test_raw_file_io(self):
         with self.open(os_helper.TESTFN, "wb", buffering=0) as f:
@@ -575,7 +577,7 @@ def test_readline(self):
             self.assertEqual(f.readline(), b"foo\x00bar\n")
             self.assertEqual(f.readline(None), b"another line")
             self.assertRaises(TypeError, f.readline, 5.3)
-        with self.open(os_helper.TESTFN, "r") as f:
+        with self.open(os_helper.TESTFN, "r", encoding="utf-8") as f:
             self.assertRaises(TypeError, f.readline, 5.3)
 
     def test_readline_nonsizeable(self):
@@ -638,7 +640,7 @@ def test_append_mode_tell(self):
             self.assertEqual(f.tell(), 3)
         with self.open(os_helper.TESTFN, "ab") as f:
             self.assertEqual(f.tell(), 3)
-        with self.open(os_helper.TESTFN, "a") as f:
+        with self.open(os_helper.TESTFN, "a", encoding="utf-8") as f:
             self.assertGreater(f.tell(), 0)
 
     def test_destructor(self):
@@ -730,13 +732,13 @@ def check(f):
 
     def test_closefd(self):
         self.assertRaises(ValueError, self.open, os_helper.TESTFN, 'w',
-                          closefd=False)
+                          encoding="utf-8", closefd=False)
 
     def test_read_closed(self):
-        with self.open(os_helper.TESTFN, "w") as f:
+        with self.open(os_helper.TESTFN, "w", encoding="utf-8") as f:
             f.write("egg\n")
-        with self.open(os_helper.TESTFN, "r") as f:
-            file = self.open(f.fileno(), "r", closefd=False)
+        with self.open(os_helper.TESTFN, "r", encoding="utf-8") as f:
+            file = self.open(f.fileno(), "r", encoding="utf-8", closefd=False)
             self.assertEqual(file.read(), "egg\n")
             file.seek(0)
             file.close()
@@ -749,14 +751,15 @@ def test_read_closed(self):
 
     def test_no_closefd_with_filename(self):
         # can't use closefd in combination with a file name
-        self.assertRaises(ValueError, self.open, os_helper.TESTFN, "r", closefd=False)
+        self.assertRaises(ValueError, self.open, os_helper.TESTFN, "r",
+                          encoding="utf-8", closefd=False)
 
     def test_closefd_attr(self):
         with self.open(os_helper.TESTFN, "wb") as f:
             f.write(b"egg\n")
-        with self.open(os_helper.TESTFN, "r") as f:
+        with self.open(os_helper.TESTFN, "r", encoding="utf-8") as f:
             self.assertEqual(f.buffer.raw.closefd, True)
-            file = self.open(f.fileno(), "r", closefd=False)
+            file = self.open(f.fileno(), "r", encoding="utf-8", closefd=False)
             self.assertEqual(file.buffer.raw.closefd, False)
 
     def test_garbage_collection(self):
@@ -821,11 +824,11 @@ def test_flush_error_on_close(self):
         self.check_flush_error_on_close(fd, 'wb', closefd=False)
         os.close(fd)
         # text io
-        self.check_flush_error_on_close(os_helper.TESTFN, 'w')
+        self.check_flush_error_on_close(os_helper.TESTFN, 'w', encoding="utf-8")
         fd = os.open(os_helper.TESTFN, os.O_WRONLY|os.O_CREAT)
-        self.check_flush_error_on_close(fd, 'w')
+        self.check_flush_error_on_close(fd, 'w', encoding="utf-8")
         fd = os.open(os_helper.TESTFN, os.O_WRONLY|os.O_CREAT)
-        self.check_flush_error_on_close(fd, 'w', closefd=False)
+        self.check_flush_error_on_close(fd, 'w', encoding="utf-8", closefd=False)
         os.close(fd)
 
     def test_multi_close(self):
@@ -860,12 +863,12 @@ def test_types_have_dict(self):
             self.assertTrue(hasattr(obj, "__dict__"))
 
     def test_opener(self):
-        with self.open(os_helper.TESTFN, "w") as f:
+        with self.open(os_helper.TESTFN, "w", encoding="utf-8") as f:
             f.write("egg\n")
         fd = os.open(os_helper.TESTFN, os.O_RDONLY)
         def opener(path, flags):
             return fd
-        with self.open("non-existent", "r", opener=opener) as f:
+        with self.open("non-existent", "r", encoding="utf-8", opener=opener) as f:
             self.assertEqual(f.read(), "egg\n")
 
     def test_bad_opener_negative_1(self):
@@ -899,12 +902,12 @@ def test_fileio_closefd(self):
     def test_nonbuffered_textio(self):
         with warnings_helper.check_no_resource_warning(self):
             with self.assertRaises(ValueError):
-                self.open(os_helper.TESTFN, 'w', buffering=0)
+                self.open(os_helper.TESTFN, 'w', encoding="utf-8", buffering=0)
 
     def test_invalid_newline(self):
         with warnings_helper.check_no_resource_warning(self):
             with self.assertRaises(ValueError):
-                self.open(os_helper.TESTFN, 'w', newline='invalid')
+                self.open(os_helper.TESTFN, 'w', encoding="utf-8", newline='invalid')
 
     def test_buffered_readinto_mixin(self):
         # Test the implementation provided by BufferedIOBase
@@ -921,31 +924,31 @@ def read(self, size):
 
     def test_fspath_support(self):
         def check_path_succeeds(path):
-            with self.open(path, "w") as f:
+            with self.open(path, "w", encoding="utf-8") as f:
                 f.write("egg\n")
 
-            with self.open(path, "r") as f:
+            with self.open(path, "r", encoding="utf-8") as f:
                 self.assertEqual(f.read(), "egg\n")
 
         check_path_succeeds(FakePath(os_helper.TESTFN))
         check_path_succeeds(FakePath(os.fsencode(os_helper.TESTFN)))
 
-        with self.open(os_helper.TESTFN, "w") as f:
+        with self.open(os_helper.TESTFN, "w", encoding="utf-8") as f:
             bad_path = FakePath(f.fileno())
             with self.assertRaises(TypeError):
-                self.open(bad_path, 'w')
+                self.open(bad_path, 'w', encoding="utf-8")
 
         bad_path = FakePath(None)
         with self.assertRaises(TypeError):
-            self.open(bad_path, 'w')
+            self.open(bad_path, 'w', encoding="utf-8")
 
         bad_path = FakePath(FloatingPointError)
         with self.assertRaises(FloatingPointError):
-            self.open(bad_path, 'w')
+            self.open(bad_path, 'w', encoding="utf-8")
 
         # ensure that refcounting is correct with some error conditions
         with self.assertRaisesRegex(ValueError, 'read/write/append mode'):
-            self.open(FakePath(os_helper.TESTFN), 'rwxa')
+            self.open(FakePath(os_helper.TESTFN), 'rwxa', encoding="utf-8")
 
     def test_RawIOBase_readall(self):
         # Exercise the default unlimited RawIOBase.read() and readall()
@@ -2590,7 +2593,7 @@ def tearDown(self):
     def test_constructor(self):
         r = self.BytesIO(b"\xc3\xa9\n\n")
         b = self.BufferedReader(r, 1000)
-        t = self.TextIOWrapper(b)
+        t = self.TextIOWrapper(b, encoding="utf-8")
         t.__init__(b, encoding="latin-1", newline="\r\n")
         self.assertEqual(t.encoding, "latin-1")
         self.assertEqual(t.line_buffering, False)
@@ -2609,7 +2612,7 @@ def test_uninitialized(self):
         self.assertRaisesRegex((ValueError, AttributeError),
                                'uninitialized|has no attribute',
                                t.read, 0)
-        t.__init__(self.MockRawIO())
+        t.__init__(self.MockRawIO(), encoding="utf-8")
         self.assertEqual(t.read(0), '')
 
     def test_non_text_encoding_codecs_are_rejected(self):
@@ -2624,7 +2627,7 @@ def test_non_text_encoding_codecs_are_rejected(self):
     def test_detach(self):
         r = self.BytesIO()
         b = self.BufferedWriter(r)
-        t = self.TextIOWrapper(b)
+        t = self.TextIOWrapper(b, encoding="ascii")
         self.assertIs(t.detach(), b)
 
         t = self.TextIOWrapper(b, encoding="ascii")
@@ -2664,7 +2667,7 @@ def test_repr(self):
     def test_recursive_repr(self):
         # Issue #25455
         raw = self.BytesIO()
-        t = self.TextIOWrapper(raw)
+        t = self.TextIOWrapper(raw, encoding="utf-8")
         with support.swap_attr(raw, 'name', t):
             try:
                 repr(t)  # Should not crash
@@ -2674,7 +2677,7 @@ def test_recursive_repr(self):
     def test_line_buffering(self):
         r = self.BytesIO()
         b = self.BufferedWriter(r, 1000)
-        t = self.TextIOWrapper(b, newline="\n", line_buffering=True)
+        t = self.TextIOWrapper(b, encoding="utf-8", newline="\n", line_buffering=True)
         t.write("X")
         self.assertEqual(r.getvalue(), b"")  # No flush happened
         t.write("Y\nZ")
@@ -2685,7 +2688,7 @@ def test_line_buffering(self):
     def test_reconfigure_line_buffering(self):
         r = self.BytesIO()
         b = self.BufferedWriter(r, 1000)
-        t = self.TextIOWrapper(b, newline="\n", line_buffering=False)
+        t = self.TextIOWrapper(b, encoding="utf-8", newline="\n", line_buffering=False)
         t.write("AB\nC")
         self.assertEqual(r.getvalue(), b"")
 
@@ -2722,7 +2725,9 @@ def test_default_encoding(self):
 
             current_locale_encoding = locale.getpreferredencoding(False)
             b = self.BytesIO()
-            t = self.TextIOWrapper(b)
+            with warnings.catch_warnings():
+                warnings.simplefilter("ignore", EncodingWarning)
+                t = self.TextIOWrapper(b)
             self.assertEqual(t.encoding, current_locale_encoding)
         finally:
             os.environ.clear()
@@ -2735,16 +2740,18 @@ def test_device_encoding(self):
         import _testcapi
         b = self.BytesIO()
         b.fileno = lambda: _testcapi.INT_MAX + 1
-        self.assertRaises(OverflowError, self.TextIOWrapper, b)
+        self.assertRaises(OverflowError, self.TextIOWrapper, b, encoding="locale")
         b.fileno = lambda: _testcapi.UINT_MAX + 1
-        self.assertRaises(OverflowError, self.TextIOWrapper, b)
+        self.assertRaises(OverflowError, self.TextIOWrapper, b, encoding="locale")
 
     def test_encoding(self):
         # Check the encoding attribute is always set, and valid
         b = self.BytesIO()
         t = self.TextIOWrapper(b, encoding="utf-8")
         self.assertEqual(t.encoding, "utf-8")
-        t = self.TextIOWrapper(b)
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore", EncodingWarning)
+            t = self.TextIOWrapper(b)
         self.assertIsNotNone(t.encoding)
         codecs.lookup(t.encoding)
 
@@ -2909,7 +2916,7 @@ def test_error_through_destructor(self):
         rawio = self.CloseFailureIO()
         with support.catch_unraisable_exception() as cm:
             with self.assertRaises(AttributeError):
-                self.TextIOWrapper(rawio).xyzzy
+                self.TextIOWrapper(rawio, encoding="utf-8").xyzzy
 
             if not IOBASE_EMITS_UNRAISABLE:
                 self.assertIsNone(cm.unraisable)
@@ -3116,11 +3123,11 @@ def test_unreadable(self):
         class UnReadable(self.BytesIO):
             def readable(self):
                 return False
-        txt = self.TextIOWrapper(UnReadable())
+        txt = self.TextIOWrapper(UnReadable(), encoding="utf-8")
         self.assertRaises(OSError, txt.read)
 
     def test_read_one_by_one(self):
-        txt = self.TextIOWrapper(self.BytesIO(b"AA\r\nBB"))
+        txt = self.TextIOWrapper(self.BytesIO(b"AA\r\nBB"), encoding="utf-8")
         reads = ""
         while True:
             c = txt.read(1)
@@ -3130,7 +3137,7 @@ def test_read_one_by_one(self):
         self.assertEqual(reads, "AA\nBB")
 
     def test_readlines(self):
-        txt = self.TextIOWrapper(self.BytesIO(b"AA\nBB\nCC"))
+        txt = self.TextIOWrapper(self.BytesIO(b"AA\nBB\nCC"), encoding="utf-8")
         self.assertEqual(txt.readlines(), ["AA\n", "BB\n", "CC"])
         txt.seek(0)
         self.assertEqual(txt.readlines(None), ["AA\n", "BB\n", "CC"])
@@ -3140,7 +3147,7 @@ def test_readlines(self):
     # read in amounts equal to TextIOWrapper._CHUNK_SIZE which is 128.
     def test_read_by_chunk(self):
         # make sure "\r\n" straddles 128 char boundary.
-        txt = self.TextIOWrapper(self.BytesIO(b"A" * 127 + b"\r\nB"))
+        txt = self.TextIOWrapper(self.BytesIO(b"A" * 127 + b"\r\nB"), encoding="utf-8")
         reads = ""
         while True:
             c = txt.read(128)
@@ -3152,7 +3159,7 @@ def test_read_by_chunk(self):
     def test_writelines(self):
         l = ['ab', 'cd', 'ef']
         buf = self.BytesIO()
-        txt = self.TextIOWrapper(buf)
+        txt = self.TextIOWrapper(buf, encoding="utf-8")
         txt.writelines(l)
         txt.flush()
         self.assertEqual(buf.getvalue(), b'abcdef')
@@ -3160,13 +3167,13 @@ def test_writelines(self):
     def test_writelines_userlist(self):
         l = UserList(['ab', 'cd', 'ef'])
         buf = self.BytesIO()
-        txt = self.TextIOWrapper(buf)
+        txt = self.TextIOWrapper(buf, encoding="utf-8")
         txt.writelines(l)
         txt.flush()
         self.assertEqual(buf.getvalue(), b'abcdef')
 
     def test_writelines_error(self):
-        txt = self.TextIOWrapper(self.BytesIO())
+        txt = self.TextIOWrapper(self.BytesIO(), encoding="utf-8")
         self.assertRaises(TypeError, txt.writelines, [1, 2, 3])
         self.assertRaises(TypeError, txt.writelines, None)
         self.assertRaises(TypeError, txt.writelines, b'abc')
@@ -3274,16 +3281,16 @@ def test_seek_append_bom(self):
                 self.assertEqual(f.read(), 'aaaxxx'.encode(charset))
 
     def test_errors_property(self):
-        with self.open(os_helper.TESTFN, "w") as f:
+        with self.open(os_helper.TESTFN, "w", encoding="utf-8") as f:
             self.assertEqual(f.errors, "strict")
-        with self.open(os_helper.TESTFN, "w", errors="replace") as f:
+        with self.open(os_helper.TESTFN, "w", encoding="utf-8", errors="replace") as f:
             self.assertEqual(f.errors, "replace")
 
     @support.no_tracing
     def test_threads_write(self):
         # Issue6750: concurrent writes could duplicate data
         event = threading.Event()
-        with self.open(os_helper.TESTFN, "w", buffering=1) as f:
+        with self.open(os_helper.TESTFN, "w", encoding="utf-8", buffering=1) as f:
             def run(n):
                 text = "Thread%03d\n" % n
                 event.wait()
@@ -3292,7 +3299,7 @@ def run(n):
                        for x in range(20)]
             with threading_helper.start_threads(threads, event.set):
                 time.sleep(0.02)
-        with self.open(os_helper.TESTFN) as f:
+        with self.open(os_helper.TESTFN, encoding="utf-8") as f:
             content = f.read()
             for n in range(20):
                 self.assertEqual(content.count("Thread%03d\n" % n), 1)
@@ -3363,7 +3370,7 @@ def test_multi_close(self):
         self.assertRaises(ValueError, txt.flush)
 
     def test_unseekable(self):
-        txt = self.TextIOWrapper(self.MockUnseekableIO(self.testdata))
+        txt = self.TextIOWrapper(self.MockUnseekableIO(self.testdata), encoding="utf-8")
         self.assertRaises(self.UnsupportedOperation, txt.tell)
         self.assertRaises(self.UnsupportedOperation, txt.seek, 0)
 
@@ -3452,11 +3459,11 @@ def test_reconfigure_write_through(self):
     def test_read_nonbytes(self):
         # Issue #17106
         # Crash when underlying read() returns non-bytes
-        t = self.TextIOWrapper(self.StringIO('a'))
+        t = self.TextIOWrapper(self.StringIO('a'), encoding="utf-8")
         self.assertRaises(TypeError, t.read, 1)
-        t = self.TextIOWrapper(self.StringIO('a'))
+        t = self.TextIOWrapper(self.StringIO('a'), encoding="utf-8")
         self.assertRaises(TypeError, t.readline)
-        t = self.TextIOWrapper(self.StringIO('a'))
+        t = self.TextIOWrapper(self.StringIO('a'), encoding="utf-8")
         self.assertRaises(TypeError, t.read)
 
     def test_illegal_encoder(self):
@@ -3724,7 +3731,7 @@ class CTextIOWrapperTest(TextIOWrapperTest):
     def test_initialization(self):
         r = self.BytesIO(b"\xc3\xa9\n\n")
         b = self.BufferedReader(r, 1000)
-        t = self.TextIOWrapper(b)
+        t = self.TextIOWrapper(b, encoding="utf-8")
         self.assertRaises(ValueError, t.__init__, b, newline='xyzzy')
         self.assertRaises(ValueError, t.read)
 
@@ -3948,7 +3955,7 @@ def test_attributes(self):
         f.close()
 
         with warnings_helper.check_warnings(('', DeprecationWarning)):
-            f = self.open(os_helper.TESTFN, "U")
+            f = self.open(os_helper.TESTFN, "U", encoding="utf-8")
         self.assertEqual(f.name,            os_helper.TESTFN)
         self.assertEqual(f.buffer.name,     os_helper.TESTFN)
         self.assertEqual(f.buffer.raw.name, os_helper.TESTFN)
@@ -3957,7 +3964,7 @@ def test_attributes(self):
         self.assertEqual(f.buffer.raw.mode, "rb")
         f.close()
 
-        f = self.open(os_helper.TESTFN, "w+")
+        f = self.open(os_helper.TESTFN, "w+", encoding="utf-8")
         self.assertEqual(f.mode,            "w+")
         self.assertEqual(f.buffer.mode,     "rb+") # Does it really matter?
         self.assertEqual(f.buffer.raw.mode, "rb+")
@@ -3974,7 +3981,7 @@ def test_open_pipe_with_append(self):
         # bpo-27805: Ignore ESPIPE from lseek() in open().
         r, w = os.pipe()
         self.addCleanup(os.close, r)
-        f = self.open(w, 'a')
+        f = self.open(w, 'a', encoding="utf-8")
         self.addCleanup(f.close)
         # Check that the file is marked non-seekable. On Windows, however, lseek
         # somehow succeeds on pipes.
@@ -3999,6 +4006,8 @@ def test_io_after_close(self):
                 {"mode": "w+", "buffering": 2},
                 {"mode": "w+b", "buffering": 0},
             ]:
+            if "b" not in kwargs["mode"]:
+                kwargs["encoding"] = "utf-8"
             f = self.open(os_helper.TESTFN, **kwargs)
             f.close()
             self.assertRaises(ValueError, f.flush)
@@ -4059,7 +4068,7 @@ def _check_abc_inheritance(self, abcmodule):
             self.assertNotIsInstance(f, abcmodule.RawIOBase)
             self.assertIsInstance(f, abcmodule.BufferedIOBase)
             self.assertNotIsInstance(f, abcmodule.TextIOBase)
-        with self.open(os_helper.TESTFN, "w") as f:
+        with self.open(os_helper.TESTFN, "w", encoding="utf-8") as f:
             self.assertIsInstance(f, abcmodule.IOBase)
             self.assertNotIsInstance(f, abcmodule.RawIOBase)
             self.assertNotIsInstance(f, abcmodule.BufferedIOBase)
@@ -4085,7 +4094,7 @@ def _check_warn_on_dealloc(self, *args, **kwargs):
     def test_warn_on_dealloc(self):
         self._check_warn_on_dealloc(os_helper.TESTFN, "wb", buffering=0)
         self._check_warn_on_dealloc(os_helper.TESTFN, "wb")
-        self._check_warn_on_dealloc(os_helper.TESTFN, "w")
+        self._check_warn_on_dealloc(os_helper.TESTFN, "w", encoding="utf-8")
 
     def _check_warn_on_dealloc_fd(self, *args, **kwargs):
         fds = []
@@ -4109,7 +4118,7 @@ def cleanup_fds():
     def test_warn_on_dealloc_fd(self):
         self._check_warn_on_dealloc_fd("rb", buffering=0)
         self._check_warn_on_dealloc_fd("rb")
-        self._check_warn_on_dealloc_fd("r")
+        self._check_warn_on_dealloc_fd("r", encoding="utf-8")
 
 
     def test_pickling(self):
@@ -4125,6 +4134,8 @@ def test_pickling(self):
                 {"mode": "w+b"},
                 {"mode": "w+b", "buffering": 0},
             ]:
+            if "b" not in kwargs["mode"]:
+                kwargs["encoding"] = "utf-8"
             for protocol in range(pickle.HIGHEST_PROTOCOL + 1):
                 with self.open(os_helper.TESTFN, **kwargs) as f:
                     self.assertRaises(TypeError, pickle.dumps, f, protocol)
@@ -4189,9 +4200,9 @@ def _test_nonblock_pipe_write(self, bufsize):
 
     def test_create_fail(self):
         # 'x' mode fails if file is existing
-        with self.open(os_helper.TESTFN, 'w'):
+        with self.open(os_helper.TESTFN, 'w', encoding="utf-8"):
             pass
-        self.assertRaises(FileExistsError, self.open, os_helper.TESTFN, 'x')
+        self.assertRaises(FileExistsError, self.open, os_helper.TESTFN, 'x', encoding="utf-8")
 
     def test_create_writes(self):
         # 'x' mode opens for writing
@@ -4202,7 +4213,7 @@ def test_create_writes(self):
 
     def test_open_allargs(self):
         # there used to be a buffer overflow in the parser for rawmode
-        self.assertRaises(ValueError, self.open, os_helper.TESTFN, 'rwax+')
+        self.assertRaises(ValueError, self.open, os_helper.TESTFN, 'rwax+', encoding="utf-8")
 
     def test_check_encoding_errors(self):
         # bpo-37388: open() and TextIOWrapper must check encoding and errors
@@ -4474,7 +4485,7 @@ def test_interrupted_read_retry_buffered(self):
 
     def test_interrupted_read_retry_text(self):
         self.check_interrupted_read_retry(lambda x: x,
-                                          mode="r")
+                                          mode="r", encoding="latin1")
 
     def check_interrupted_write_retry(self, item, **fdopen_kwargs):
         """Check that a buffered write, when it gets interrupted (either