diff --git a/CHANGES.rst b/CHANGES.rst
index 232b144a5c..723af0729f 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -28,6 +28,7 @@ Unreleased
     it's disabled in config. Previously, only disabling worked. :issue:`5916`
 -   ``Flask.select_jinja_autoescape`` uses case-insensitive comparison instead
     of only lower case file extensions. :pr:`6012`
+-   Fix compatibility with pytest-9.1 by removing use of private API. :issue:`6071`
 
 
 Version 3.1.3
diff --git a/tests/conftest.py b/tests/conftest.py
index 0414b9e22f..e7fad0f861 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -2,43 +2,26 @@
 import sys
 
 import pytest
-from _pytest import monkeypatch
 
 from flask import Flask
 from flask.globals import app_ctx as _app_ctx
 
 
-@pytest.fixture(scope="session", autouse=True)
-def _standard_os_environ():
-    """Set up ``os.environ`` at the start of the test session to have
-    standard values. Returns a list of operations that is used by
-    :func:`._reset_os_environ` after each test.
-    """
-    mp = monkeypatch.MonkeyPatch()
-    out = (
-        (os.environ, "FLASK_ENV_FILE", monkeypatch.notset),
-        (os.environ, "FLASK_APP", monkeypatch.notset),
-        (os.environ, "FLASK_DEBUG", monkeypatch.notset),
-        (os.environ, "FLASK_RUN_FROM_CLI", monkeypatch.notset),
-        (os.environ, "WERKZEUG_RUN_MAIN", monkeypatch.notset),
-    )
-
-    for _, key, value in out:
-        if value is monkeypatch.notset:
-            mp.delenv(key, False)
-        else:
-            mp.setenv(key, value)
-
-    yield out
-    mp.undo()
-
-
 @pytest.fixture(autouse=True)
-def _reset_os_environ(monkeypatch, _standard_os_environ):
-    """Reset ``os.environ`` to the standard environ after each test,
-    in case a test changed something without cleaning up.
+def _standard_os_environ(monkeypatch):
+    """Set up ``os.environ`` at the start of every test to have
+    standard values.
     """
-    monkeypatch._setitem.extend(_standard_os_environ)
+    for key in (
+        "FLASK_ENV_FILE",
+        "FLASK_APP",
+        "FLASK_DEBUG",
+        "FLASK_RUN_FROM_CLI",
+        "WERKZEUG_RUN_MAIN",
+    ):
+        monkeypatch.delenv(key, False)
+
+    yield
 
 
 @pytest.fixture
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 2a34088bd5..f3b9a8504d 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -11,7 +11,6 @@
 
 import click
 import pytest
-from _pytest.monkeypatch import notset
 from click.testing import CliRunner
 
 from flask import Blueprint
@@ -535,9 +534,8 @@ def dotenv_not_available():
 
 @need_dotenv
 def test_load_dotenv(monkeypatch):
-    # can't use monkeypatch.delitem since the keys don't exist yet
     for item in ("FOO", "BAR", "SPAM", "HAM"):
-        monkeypatch._setitem.append((os.environ, item, notset))
+        monkeypatch.delenv(item, False)
 
     monkeypatch.setenv("EGGS", "3")
     monkeypatch.chdir(test_path)
@@ -560,7 +558,7 @@ def test_load_dotenv(monkeypatch):
 @need_dotenv
 def test_dotenv_path(monkeypatch):
     for item in ("FOO", "BAR", "EGGS"):
-        monkeypatch._setitem.append((os.environ, item, notset))
+        monkeypatch.delenv(item, False)
 
     load_dotenv(test_path / ".flaskenv")
     assert Path.cwd() == cwd
@@ -568,6 +566,7 @@ def test_dotenv_path(monkeypatch):
 
 
 def test_dotenv_optional(monkeypatch):
+    monkeypatch.delenv("FOO", False)
     monkeypatch.setitem(sys.modules, "dotenv", None)
     monkeypatch.chdir(test_path)
     load_dotenv()
@@ -576,6 +575,7 @@ def test_dotenv_optional(monkeypatch):
 
 @need_dotenv
 def test_disable_dotenv_from_env(monkeypatch, runner):
+    monkeypatch.delenv("FOO", False)
     monkeypatch.chdir(test_path)
     monkeypatch.setitem(os.environ, "FLASK_SKIP_DOTENV", "1")
     runner.invoke(FlaskGroup())