diff --git a/src/_pytest/pytester.py b/src/_pytest/pytester.py
index a9299944dec..3df52ebe88c 100644
--- a/src/_pytest/pytester.py
+++ b/src/_pytest/pytester.py
@@ -6,6 +6,7 @@
 import contextlib
 import gc
 import importlib
+import locale
 import os
 import platform
 import re
@@ -129,6 +130,7 @@ def get_open_files(self) -> List[Tuple[str, str]]:
             stderr=subprocess.DEVNULL,
             check=True,
             text=True,
+            encoding=locale.getpreferredencoding(False),
         ).stdout
 
         def isopen(line: str) -> bool:
diff --git a/testing/test_parseopt.py b/testing/test_parseopt.py
index 992f49bc53c..c051ec33834 100644
--- a/testing/test_parseopt.py
+++ b/testing/test_parseopt.py
@@ -1,4 +1,5 @@
 import argparse
+import locale
 import os
 import shlex
 import subprocess
@@ -289,6 +290,10 @@ def test_multiple_metavar_help(self, parser: parseopt.Parser) -> None:
 
 
 def test_argcomplete(pytester: Pytester, monkeypatch: MonkeyPatch) -> None:
+    try:
+        encoding = locale.getencoding()  # New in Python 3.11, ignores utf-8 mode
+    except AttributeError:
+        encoding = locale.getpreferredencoding(False)
     try:
         bash_version = subprocess.run(
             ["bash", "--version"],
@@ -296,6 +301,7 @@ def test_argcomplete(pytester: Pytester, monkeypatch: MonkeyPatch) -> None:
             stderr=subprocess.DEVNULL,
             check=True,
             text=True,
+            encoding=encoding,
         ).stdout
     except (OSError, subprocess.CalledProcessError):
         pytest.skip("bash is not available")