diff --git a/Lib/os.py b/Lib/os.py
index ca418edbc57366..7b19073b043410 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -715,7 +715,9 @@ def setdefault(self, key, value):
 try:
     _putenv = putenv
 except NameError:
-    _putenv = lambda key, value: None
+    def _putenv(key, value):
+        # do nothing
+        return
 else:
     if "putenv" not in __all__:
         __all__.append("putenv")
@@ -723,7 +725,17 @@ def setdefault(self, key, value):
 try:
     _unsetenv = unsetenv
 except NameError:
-    _unsetenv = lambda key: _putenv(key, "")
+    if name == 'nt':
+        def unsetenv(key):
+            """Delete an environment variable."""
+            _putenv(key, "")
+
+        if "unsetenv" not in __all__:
+            __all__.append("unsetenv")
+        _unsetenv = unsetenv
+    else:
+        def _unsetenv(key):
+            _putenv(key, "")
 else:
     if "unsetenv" not in __all__:
         __all__.append("unsetenv")
diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index 661d91afb7eb6f..aa4756a620aae5 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -6125,43 +6125,7 @@ os_putenv(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 
 #endif /* defined(HAVE_PUTENV) && !defined(MS_WINDOWS) */
 
-#if defined(MS_WINDOWS)
-
-PyDoc_STRVAR(os_unsetenv__doc__,
-"unsetenv($module, name, /)\n"
-"--\n"
-"\n"
-"Delete an environment variable.");
-
-#define OS_UNSETENV_METHODDEF    \
-    {"unsetenv", (PyCFunction)os_unsetenv, METH_O, os_unsetenv__doc__},
-
-static PyObject *
-os_unsetenv_impl(PyObject *module, PyObject *name);
-
-static PyObject *
-os_unsetenv(PyObject *module, PyObject *arg)
-{
-    PyObject *return_value = NULL;
-    PyObject *name;
-
-    if (!PyUnicode_Check(arg)) {
-        _PyArg_BadArgument("unsetenv", "argument", "str", arg);
-        goto exit;
-    }
-    if (PyUnicode_READY(arg) == -1) {
-        goto exit;
-    }
-    name = arg;
-    return_value = os_unsetenv_impl(module, name);
-
-exit:
-    return return_value;
-}
-
-#endif /* defined(MS_WINDOWS) */
-
-#if (defined(HAVE_UNSETENV) && !defined(MS_WINDOWS))
+#if defined(HAVE_UNSETENV)
 
 PyDoc_STRVAR(os_unsetenv__doc__,
 "unsetenv($module, name, /)\n"
@@ -6193,7 +6157,7 @@ os_unsetenv(PyObject *module, PyObject *arg)
     return return_value;
 }
 
-#endif /* (defined(HAVE_UNSETENV) && !defined(MS_WINDOWS)) */
+#endif /* defined(HAVE_UNSETENV) */
 
 PyDoc_STRVAR(os_strerror__doc__,
 "strerror($module, code, /)\n"
@@ -8809,4 +8773,4 @@ os__remove_dll_directory(PyObject *module, PyObject *const *args, Py_ssize_t nar
 #ifndef OS__REMOVE_DLL_DIRECTORY_METHODDEF
     #define OS__REMOVE_DLL_DIRECTORY_METHODDEF
 #endif /* !defined(OS__REMOVE_DLL_DIRECTORY_METHODDEF) */
-/*[clinic end generated code: output=6e739a2715712e88 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=51ba5b9536420cea input=a9049054013a1b77]*/
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 5a0c8a311a790e..82becf67d3fc60 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -10180,51 +10180,7 @@ os_putenv_impl(PyObject *module, PyObject *name, PyObject *value)
 #endif /* HAVE_PUTENV */
 
 
-#ifdef MS_WINDOWS
-/*[clinic input]
-os.unsetenv
-    name: unicode
-    /
-
-Delete an environment variable.
-[clinic start generated code]*/
-
-static PyObject *
-os_unsetenv_impl(PyObject *module, PyObject *name)
-/*[clinic end generated code: output=54c4137ab1834f02 input=4d6a1747cc526d2f]*/
-{
-    /* PyUnicode_AsWideCharString() rejects embedded null characters */
-    wchar_t *name_str = PyUnicode_AsWideCharString(name, NULL);
-    if (name_str == NULL) {
-        return NULL;
-    }
-
-    BOOL ok = SetEnvironmentVariableW(name_str, NULL);
-    PyMem_Free(name_str);
-
-    if (!ok) {
-        return PyErr_SetFromWindowsErr(0);
-    }
-
-#ifdef PY_PUTENV_DICT
-    /* Remove the key from putenv_dict;
-     * this will cause it to be collected.  This has to
-     * happen after the real unsetenv() call because the
-     * old value was still accessible until then.
-     */
-    if (PyDict_DelItem(_posixstate(module)->putenv_dict, name)) {
-        /* really not much we can do; just leak */
-        if (!PyErr_ExceptionMatches(PyExc_KeyError)) {
-            return NULL;
-        }
-        PyErr_Clear();
-    }
-#endif
-
-    Py_RETURN_NONE;
-}
-/* repeat !defined(MS_WINDOWS) to workaround an Argument Clinic issue */
-#elif defined(HAVE_UNSETENV) && !defined(MS_WINDOWS)
+#ifdef HAVE_UNSETENV
 /*[clinic input]
 os.unsetenv
     name: FSConverter
@@ -10237,14 +10193,13 @@ static PyObject *
 os_unsetenv_impl(PyObject *module, PyObject *name)
 /*[clinic end generated code: output=54c4137ab1834f02 input=2bb5288a599c7107]*/
 {
-#ifndef HAVE_BROKEN_UNSETENV
-    int err;
-#endif
-
+    /* On Windows, this function is not implemented in C, but in os.py as
+       posix.putenv(name, ""). _wputenv() is preferred since it updates the
+       CRT, whereas SetEnvironmentVariableW(name, NULL) does not. */
 #ifdef HAVE_BROKEN_UNSETENV
     unsetenv(PyBytes_AS_STRING(name));
 #else
-    err = unsetenv(PyBytes_AS_STRING(name));
+    int err = unsetenv(PyBytes_AS_STRING(name));
     if (err)
         return posix_error();
 #endif