diff --git a/addons/website/tests/test_views.py b/addons/website/tests/test_views.py
index 393001f1b3a..bb7f08d2a2b 100644
--- a/addons/website/tests/test_views.py
+++ b/addons/website/tests/test_views.py
@@ -2,13 +2,14 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from hashlib import sha256
+import copy
 import unittest
 from unittest.mock import patch
 from itertools import zip_longest
 from lxml import etree as ET, html
 from lxml.html import builder as h
 
-from odoo.modules.module import _DEFAULT_MANIFEST, get_manifest
+from odoo.modules.module import _DEFAULT_MANIFEST
 from odoo.tests import common, HttpCase, tagged
 
 
@@ -1510,10 +1511,9 @@ class TestThemeViews(common.TransactionCase):
         main_view.with_context(website_id=website_1.id).arch = '<body>specific</body>'
 
         # 2. Simulate a theme install with a child view of `main_view`
+        patcher = patch('odoo.modules.module._get_manifest_cached', return_value=copy.deepcopy(_DEFAULT_MANIFEST))
+        self.startPatcher(patcher)
         test_theme_module = self.env['ir.module.module'].create({'name': 'test_theme'})
-        # Themes are required to have a valid manifest, including a `new_page_templates` property.
-        # This theme is created in python and therefore has no manifest.
-        get_manifest('test_theme').update(_DEFAULT_MANIFEST)
         self.env['ir.model.data'].create({
             'module': 'base',
             'name': 'module_test_theme_module',
diff --git a/odoo/addons/base/tests/test_module.py b/odoo/addons/base/tests/test_module.py
index 1d2009db54c..b37c72e9485 100644
--- a/odoo/addons/base/tests/test_module.py
+++ b/odoo/addons/base/tests/test_module.py
@@ -7,6 +7,7 @@ from unittest.mock import patch
 
 import odoo.addons
 from odoo.modules.module import load_manifest
+from odoo.modules.module import get_manifest
 from odoo.release import major_version
 from odoo.tests.common import BaseCase
 
@@ -71,6 +72,14 @@ class TestModuleManifest(BaseCase):
             'website': '',
         })
 
+    def test_change_manifest(self):
+        module_name = 'base'
+        new_manifest = get_manifest(module_name)
+        orig_auto_install = new_manifest['auto_install']
+        new_manifest['auto_install'] = not orig_auto_install
+        self.assertNotEqual(new_manifest, get_manifest(module_name))
+        self.assertEqual(orig_auto_install, get_manifest(module_name)['auto_install'])
+
     def test_missing_manifest(self):
         with self.assertLogs('odoo.modules.module', 'DEBUG') as capture:
             manifest = load_manifest(self.module_name)
diff --git a/odoo/modules/module.py b/odoo/modules/module.py
index a12fd5e9a41..c93a630c0d4 100644
--- a/odoo/modules/module.py
+++ b/odoo/modules/module.py
@@ -312,6 +312,7 @@ def load_manifest(module, mod_path=None):
         return {}
 
     manifest = copy.deepcopy(_DEFAULT_MANIFEST)
+
     manifest['icon'] = get_module_icon(module)
 
     with tools.file_open(manifest_file, mode='r') as f:
@@ -352,7 +353,6 @@ def load_manifest(module, mod_path=None):
 
     return manifest
 
-@functools.lru_cache(maxsize=None)
 def get_manifest(module, mod_path=None):
     """
     Get the module manifest.
@@ -365,6 +365,10 @@ def get_manifest(module, mod_path=None):
         when the manifest was not found.
     :rtype: dict
     """
+    return copy.deepcopy(_get_manifest_cached(module, mod_path))
+
+@functools.lru_cache(maxsize=None)
+def _get_manifest_cached(module, mod_path=None):
     return load_manifest(module, mod_path)
 
 def load_information_from_description_file(module, mod_path=None):