diff --git a/CHANGES.md b/CHANGES.md
index 4b5a291c7b9..2961dbb320b 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -7,6 +7,10 @@
 - Fix missing modules in self-contained binaries (#2466)
 - Fix missing toml extra used during installation (#2475)
 
+### Tests
+
+- Fix patching of `io.TextIOWrapper` (#2489)
+
 ## 21.8b0
 
 ### _Black_
diff --git a/tests/test_black.py b/tests/test_black.py
index 398a528bee9..9d590c1c03d 100644
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -25,7 +25,7 @@
 )
 import pytest
 import unittest
-from unittest.mock import patch, MagicMock
+from unittest.mock import patch, MagicMock, Mock
 from parameterized import parameterized
 
 import click
@@ -1689,7 +1689,9 @@ def test_reformat_one_with_stdin_and_existing_path(self) -> None:
 
     def test_reformat_one_with_stdin_empty(self) -> None:
         output = io.StringIO()
-        with patch("io.TextIOWrapper", lambda *args, **kwargs: output):
+        mock_io = Mock()
+        mock_io.TextIOWrapper.return_value = output
+        with patch.object(black, "io", mock_io):
             try:
                 black.format_stdin_to_stdout(
                     fast=True,