diff --git a/fieldservice_activity/models/fsm_activity.py b/fieldservice_activity/models/fsm_activity.py
index ae1f1df667..cb874629e8 100644
--- a/fieldservice_activity/models/fsm_activity.py
+++ b/fieldservice_activity/models/fsm_activity.py
@@ -1,28 +1,21 @@
 # Copyright (C) 2019 Open Source Integrators
 # License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl.html).
 
-from odoo import fields, models
+from odoo import _, fields, models
+from odoo.exceptions import ValidationError
 
 
 class FSMActivity(models.Model):
     _name = "fsm.activity"
     _description = "Field Service Activity"
 
-    name = fields.Char(
-        required=True, readonly=True, states={"todo": [("readonly", False)]}
-    )
-    required = fields.Boolean(
-        default=False,
-        readonly=True,
-        states={"todo": [("readonly", False)]},
-    )
+    name = fields.Char(required=True)
+    required = fields.Boolean()
     sequence = fields.Integer()
-    completed = fields.Boolean(default=False)
+    completed = fields.Boolean()
     completed_on = fields.Datetime(readonly=True)
     completed_by = fields.Many2one("res.users", readonly=True)
-    ref = fields.Char(
-        "Reference", readonly=True, states={"todo": [("readonly", False)]}
-    )
+    ref = fields.Char("Reference")
     fsm_order_id = fields.Many2one("fsm.order", "FSM Order")
     fsm_template_id = fields.Many2one("fsm.template", "FSM Template")
     state = fields.Selection(
@@ -31,6 +24,32 @@ class FSMActivity(models.Model):
         default="todo",
     )
 
+    @property
+    def _protected_fields(self) -> tuple[str]:
+        """Fields that should not be modified on a "done" activity"""
+        return ("name", "required", "ref")
+
+    def write(self, vals):
+        if any(fname in vals for fname in self._protected_fields) and any(
+            rec.state != "todo" for rec in self.with_context(prefetch_fields=False)
+        ):
+            fnames = list(set(self._protected_fields) & set(vals.keys()))
+            field_strings = [
+                self._fields[fname]._description_string(self.env) for fname in fnames
+            ]
+            state_string = dict(
+                self._fields["state"]._description_selection(self.env)
+            ).get(self.state)
+            raise ValidationError(
+                _(
+                    "It is forbidden to modify the following fields in a %(state)r "
+                    "Activity:\n%(fields)s",
+                    state=state_string,
+                    fields="\n".join(field_strings),
+                )
+            )
+        return super().write(vals)
+
     def action_done(self):
         self.write(
             {
diff --git a/fieldservice_activity/views/fsm_order.xml b/fieldservice_activity/views/fsm_order.xml
index 4f984b5d87..b777b75dca 100644
--- a/fieldservice_activity/views/fsm_order.xml
+++ b/fieldservice_activity/views/fsm_order.xml
@@ -10,9 +10,9 @@
                     <field name="order_activity_ids" nolabel="1">
                         <tree editable="bottom">
                             <field name="sequence" widget="handle" />
-                            <field name="name" />
-                            <field name="required" />
-                            <field name="ref" />
+                            <field name="name" readonly="state != 'todo'" />
+                            <field name="required" readonly="state != 'todo'" />
+                            <field name="ref" readonly="state != 'todo'" />
                             <field name="completed" column_invisible="1" />
                             <field name="completed_on" />
                             <field name="completed_by" />
diff --git a/fieldservice_activity/views/fsm_template.xml b/fieldservice_activity/views/fsm_template.xml
index 048a4c0215..491ed73a11 100644
--- a/fieldservice_activity/views/fsm_template.xml
+++ b/fieldservice_activity/views/fsm_template.xml
@@ -10,9 +10,9 @@
                     <field name="temp_activity_ids" nolabel="1">
                         <tree editable="bottom">
                             <field name="sequence" widget="handle" />
-                            <field name="name" />
-                            <field name="required" />
-                            <field name="ref" />
+                            <field name="name" readonly="state != 'todo'" />
+                            <field name="required" readonly="state != 'todo'" />
+                            <field name="ref" readonly="state != 'todo'" />
                             <field name="completed" invisible="1" />
                             <field name="completed_on" invisible="1" />
                             <field name="completed_by" invisible="1" />