diff --git a/addons/project/tests/__init__.py b/addons/project/tests/__init__.py
index 6f85611241d..8aea3e56d27 100644
--- a/addons/project/tests/__init__.py
+++ b/addons/project/tests/__init__.py
@@ -7,6 +7,7 @@ from . import test_project_config
 from . import test_project_flow
 from . import test_project_recurrence
 from . import test_project_sharing
+from . import test_project_sharing_portal_access
 from . import test_project_sharing_ui
 from . import test_project_subtasks
 from . import test_project_ui
diff --git a/addons/project/tests/test_project_sharing.py b/addons/project/tests/test_project_sharing.py
index 0a4828b4a96..5846fc77f0e 100644
--- a/addons/project/tests/test_project_sharing.py
+++ b/addons/project/tests/test_project_sharing.py
@@ -51,10 +51,12 @@ class TestProjectSharingCommon(TestProjectCommon):
             'project_id': cls.project_portal.id,
         })
 
+        cls.project_sharing_form_view_xml_id = 'project.project_sharing_project_task_view_form'
+
     def get_project_sharing_form_view(self, record, with_user=None):
         return Form(
             record.with_user(with_user or self.env.user),
-            view="project.project_sharing_project_task_view_form"
+            view=self.project_sharing_form_view_xml_id
         )
 
 @tagged('project_sharing')
diff --git a/addons/project/tests/test_project_sharing_portal_access.py b/addons/project/tests/test_project_sharing_portal_access.py
new file mode 100644
index 00000000000..f7cfed90e29
--- /dev/null
+++ b/addons/project/tests/test_project_sharing_portal_access.py
@@ -0,0 +1,76 @@
+# -*- coding: utf-8 -*-
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from collections import OrderedDict
+from odoo import Command
+from odoo.exceptions import AccessError
+from odoo.tests import tagged
+
+from .test_project_sharing import TestProjectSharingCommon
+
+
+@tagged('post_install', '-at_install')
+class TestProjectSharingPortalAccess(TestProjectSharingCommon):
+
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        project_share_wizard = cls.env['project.share.wizard'].create({
+            'access_mode': 'edit',
+            'res_model': 'project.project',
+            'res_id': cls.project_portal.id,
+            'partner_ids': [
+                Command.link(cls.partner_portal.id),
+            ],
+        })
+        project_share_wizard.action_send_mail()
+
+        Task = cls.env['project.task']
+        cls.read_protected_fields_task = OrderedDict([
+            (k, v)
+            for k, v in Task._fields.items()
+            if k in Task.SELF_READABLE_FIELDS
+        ])
+        cls.write_protected_fields_task = OrderedDict([
+            (k, v)
+            for k, v in Task._fields.items()
+            if k in Task.SELF_WRITABLE_FIELDS
+        ])
+        cls.readonly_protected_fields_task = OrderedDict([
+            (k, v)
+            for k, v in Task._fields.items()
+            if k in Task.SELF_READABLE_FIELDS and k not in Task.SELF_WRITABLE_FIELDS
+        ])
+        cls.other_fields_task = OrderedDict([
+            (k, v)
+            for k, v in Task._fields.items()
+            if k not in Task.SELF_READABLE_FIELDS
+        ])
+
+    def test_readonly_fields(self):
+        """ The fields are not writeable should not be editable by the portal user. """
+        view_infos = self.task_portal.fields_view_get(view_id=self.env.ref(self.project_sharing_form_view_xml_id).id)
+        project_task_fields = {
+            field_name
+            for field_name, field_attrs in view_infos['fields'].items()
+            if field_name not in self.write_protected_fields_task
+        }
+        with self.get_project_sharing_form_view(self.task_portal, self.user_portal) as form:
+            for field in project_task_fields:
+                with self.assertRaises(AssertionError, msg="Field '%s' should be readonly in the project sharing form view "):
+                    form.__setattr__(field, 'coucou')
+
+    def test_read_task_with_portal_user(self):
+        self.task_portal.with_user(self.user_portal).read(self.read_protected_fields_task)
+
+        with self.assertRaises(AccessError):
+            self.task_portal.with_user(self.user_portal).read(self.other_fields_task)
+
+    def test_write_with_portal_user(self):
+        for field in self.readonly_protected_fields_task:
+            with self.assertRaises(AccessError):
+                self.task_portal.with_user(self.user_portal).write({field: 'dummy'})
+
+        for field in self.other_fields_task:
+            with self.assertRaises(AccessError):
+                self.task_portal.with_user(self.user_portal).write({field: 'dummy'})