diff --git a/sale_substate/models/sale_order.py b/sale_substate/models/sale_order.py
index 66409eb8a48..9954799a870 100644
--- a/sale_substate/models/sale_order.py
+++ b/sale_substate/models/sale_order.py
@@ -13,5 +13,5 @@ class BaseSubstateType(models.Model):
 
 
 class SaleOrder(models.Model):
-    _inherit = ["sale.order", "base.substate.mixin"]
+    _inherit = ["base.substate.mixin", "sale.order"]  # order matters
     _name = "sale.order"
diff --git a/sale_substate/tests/test_sale_substate.py b/sale_substate/tests/test_sale_substate.py
index b363e372569..5a97e506f44 100644
--- a/sale_substate/tests/test_sale_substate.py
+++ b/sale_substate/tests/test_sale_substate.py
@@ -61,6 +61,15 @@ def test_sale_order_substate(self):
         self.assertTrue(so_test1.state == "sale")
         self.assertTrue(so_test1.substate_id == self.substate_valid_docs)
 
+        # manually change the substate; this one has a mail template
+        self.env.cr.flush()  # this is to post the messages (it's in after commit hook)
+        messages = so_test1.message_ids
+        so_test1.write({"substate_id": self.substate_in_delivery.id})
+        self.env.cr.flush()  # this is to post the messages (again)
+        new_messages = so_test1.message_ids - messages
+        expected_msg = "You order is being prepared for delivery."
+        self.assertTrue(expected_msg in "".join(new_messages.mapped("body")))
+
         # Test that substate_id is set to false if
         # there is not substate corresponding to state
         so_test1._action_cancel()
diff --git a/test-requirements.txt b/test-requirements.txt
index 66bc2cbae3f..0dba0438eaa 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -1 +1,2 @@
 odoo_test_helper
+git+https://github.com/lambdao-dev/server-ux@17.0-fxsbsttmx-len#subdirectory=base_substate  # to remove once merged