diff --git a/doc/en/builtin.rst b/doc/en/builtin.rst
index ea2f27a4c..99bc951b5 100644
--- a/doc/en/builtin.rst
+++ b/doc/en/builtin.rst
@@ -132,7 +132,7 @@ For information about fixtures, see :ref:`fixtures`. To see a complete list of a
             monkeypatch.delattr(obj, name, raising=True)
             monkeypatch.setitem(mapping, name, value)
             monkeypatch.delitem(obj, name, raising=True)
-            monkeypatch.setenv(name, value, prepend=False)
+            monkeypatch.setenv(name, value, prepend=None)
             monkeypatch.delenv(name, raising=True)
             monkeypatch.syspath_prepend(path)
             monkeypatch.chdir(path)
diff --git a/doc/en/how-to/monkeypatch.rst b/doc/en/how-to/monkeypatch.rst
index 4f9b5aa99..8c5f676b9 100644
--- a/doc/en/how-to/monkeypatch.rst
+++ b/doc/en/how-to/monkeypatch.rst
@@ -21,7 +21,7 @@ functionality in tests:
     monkeypatch.delattr(obj, name, raising=True)
     monkeypatch.setitem(mapping, name, value)
     monkeypatch.delitem(obj, name, raising=True)
-    monkeypatch.setenv(name, value, prepend=False)
+    monkeypatch.setenv(name, value, prepend=None)
     monkeypatch.delenv(name, raising=True)
     monkeypatch.syspath_prepend(path)
     monkeypatch.chdir(path)
diff --git a/src/_pytest/monkeypatch.py b/src/_pytest/monkeypatch.py
index 708b25aa0..e39712a90 100644
--- a/src/_pytest/monkeypatch.py
+++ b/src/_pytest/monkeypatch.py
@@ -36,7 +36,7 @@ def monkeypatch() -> Generator["MonkeyPatch", None, None]:
         monkeypatch.delattr(obj, name, raising=True)
         monkeypatch.setitem(mapping, name, value)
         monkeypatch.delitem(obj, name, raising=True)
-        monkeypatch.setenv(name, value, prepend=False)
+        monkeypatch.setenv(name, value, prepend=None)
         monkeypatch.delenv(name, raising=True)
         monkeypatch.syspath_prepend(path)
         monkeypatch.chdir(path)