diff --git a/odoo/addons/base/models/ir_model.py b/odoo/addons/base/models/ir_model.py
index dfb0238e327..2f4ffb39f31 100644
--- a/odoo/addons/base/models/ir_model.py
+++ b/odoo/addons/base/models/ir_model.py
@@ -244,8 +244,7 @@ class IrModel(models.Model):
     def _check_model_name(self):
         for model in self:
             if model.state == 'manual':
-                if not model.model.startswith('x_'):
-                    raise ValidationError(_("The model name must start with 'x_'."))
+                self._check_manual_name(model.model)
             if not models.check_object_name(model.model):
                 raise ValidationError(_("The model name can only contain lowercase characters, digits, underscores and dots."))
 
@@ -443,6 +442,15 @@ class IrModel(models.Model):
 
         return CustomModel
 
+    @api.model
+    def _is_manual_name(self, name):
+        return name.startswith('x_')
+
+    @api.model
+    def _check_manual_name(self, name):
+        if not self._is_manual_name(name):
+            raise ValidationError(_("The model name must start with 'x_'."))
+
     def _add_manual_models(self):
         """ Add extra models to the registry. """
         # clean up registry first
@@ -1255,7 +1263,7 @@ class IrModelFields(models.Model):
         elif field_data['ttype'] == 'monetary':
             # be sure that custom monetary field are always instanciated
             if not self.pool.loaded and \
-                not (field_data['currency_field'] and field_data['currency_field'].startswith('x_')):
+                not (field_data['currency_field'] and self._is_manual_name(field_data['currency_field'])):
                 return
             attrs['currency_field'] = field_data['currency_field']
         # add compute function if given
@@ -1269,6 +1277,10 @@ class IrModelFields(models.Model):
         if attrs:
             return fields.Field.by_type[field_data['ttype']](**attrs)
 
+    @api.model
+    def _is_manual_name(self, name):
+        return name.startswith('x_')
+
     def _add_manual_fields(self, model):
         """ Add extra fields on model. """
         fields_data = self._get_manual_field_data(model._name)
diff --git a/odoo/models.py b/odoo/models.py
index 24c38cea41a..944028f929b 100644
--- a/odoo/models.py
+++ b/odoo/models.py
@@ -645,7 +645,7 @@ class BaseModel(metaclass=MetaModel):
             isinstance(getattr(model, name, None), fields.Field)
             for model in [cls] + [self.env.registry[inherit] for inherit in cls._inherits]
         )
-        if not (is_class_field or name.startswith('x_')):
+        if not (is_class_field or self.env['ir.model.fields']._is_manual_name(name)):
             raise ValidationError(
                 f"The field `{name}` is not defined in the `{cls._name}` Python class and does not start with 'x_'"
             )