diff --git a/odoo/addons/test_new_api/models/test_new_api.py b/odoo/addons/test_new_api/models/test_new_api.py
index 13485aa9aee..9104a5662da 100644
--- a/odoo/addons/test_new_api/models/test_new_api.py
+++ b/odoo/addons/test_new_api/models/test_new_api.py
@@ -159,7 +159,7 @@ class Message(models.Model):
     @api.depends('discussion.messages.important')
     def _compute_has_important_sibling(self):
         for record in self:
-            siblings = record.discussion.messages - record
+            siblings = record.discussion.with_context(active_test=False).messages - record
             record.has_important_sibling = any(siblings.mapped('important'))
 
     @api.constrains('author', 'discussion')
diff --git a/odoo/addons/test_new_api/tests/test_onchange.py b/odoo/addons/test_new_api/tests/test_onchange.py
index 2fdd9ba7c43..5343cbcafe9 100644
--- a/odoo/addons/test_new_api/tests/test_onchange.py
+++ b/odoo/addons/test_new_api/tests/test_onchange.py
@@ -1252,3 +1252,22 @@ class TestComputeOnchange2(common.TransactionCase):
                 self.assertEqual(message_form.has_important_sibling, True)
                 message_form.body = 'Required Body'
             self.assertEqual(len(discussion_form.messages), 2)
+
+        # Test the same flow but when the important message is archived.
+        # The _compute_has_important_sibling should take in account archived siblings.
+        discussion = self.env['test_new_api.discussion'].create({
+            'messages': [
+                Command.create({'body': 'Archived Important sibling', 'important': True, 'active': False}),
+            ],
+            'name': 'Required field',
+            'participants': [Command.set(self.env.user.ids)],
+        })
+
+        with Form(discussion, 'test_new_api.discussion_form_2') as discussion_form:
+            self.assertEqual(len(discussion_form.messages), 0)
+            with discussion_form.messages.new() as message_form:
+                # this actually checks that during the onchange, the new message
+                # has access to its archived sibling messages through the discussion
+                self.assertEqual(message_form.has_important_sibling, True)
+                message_form.body = 'Required Body'
+            self.assertEqual(len(discussion_form.messages), 1)
diff --git a/odoo/fields.py b/odoo/fields.py
index 3a6463ab011..69695c69a35 100644
--- a/odoo/fields.py
+++ b/odoo/fields.py
@@ -4159,12 +4159,11 @@ class _RelationalMulti(_Relational):
 
     def _update(self, records, value):
         """ Update the cached value of ``self`` for ``records`` with ``value``. """
-        if value:
-            cache = records.env.cache
-            for record in records:
-                val = self.convert_to_cache(record[self.name] | value, record, validate=False)
-                cache.set(record, self, val)
-            records.modified([self.name])
+        cache = records.env.cache
+        for record in records.with_context(active_test=False):
+            val = self.convert_to_cache(record[self.name] | value, record, validate=False)
+            cache.set(record, self, val)
+        records.modified([self.name])
 
     def convert_to_cache(self, value, record, validate=True):
         # cache format: tuple(ids)