diff --git a/addons/event_sale/models/event_registration.py b/addons/event_sale/models/event_registration.py
index e765e016035..9300d610790 100644
--- a/addons/event_sale/models/event_registration.py
+++ b/addons/event_sale/models/event_registration.py
@@ -28,13 +28,14 @@ class EventRegistration(models.Model):
     def _compute_registration_status(self):
         self.filtered(lambda reg: not reg.state).state = 'draft'
         for so_line, registrations in self.grouped('sale_order_line_id').items():
-            cancelled_registrations = registrations.filtered(lambda reg: reg.sale_order_id.state == 'cancel')
-            cancelled_registrations.state = 'cancel'
+            cancelled_so_registrations = registrations.filtered(lambda reg: reg.sale_order_id.state == 'cancel')
+            cancelled_so_registrations.state = 'cancel'
+            cancelled_registrations = cancelled_so_registrations | registrations.filtered(lambda reg: reg.state == 'cancel')
             if not so_line or float_is_zero(so_line.price_total, precision_digits=so_line.currency_id.rounding):
                 registrations.sale_status = 'free'
                 registrations.filtered(lambda reg: reg.state == 'draft').write({"state": "open"})
             else:
-                sold_registrations = registrations.filtered(lambda reg: reg.sale_order_id.state == 'sale')
+                sold_registrations = registrations.filtered(lambda reg: reg.sale_order_id.state == 'sale') - cancelled_registrations
                 sold_registrations.sale_status = 'sold'
                 (registrations - sold_registrations).sale_status = 'to_pay'
                 sold_registrations.filtered(lambda reg: reg.state in {'draft', 'cancel'}).write({"state": "open"})
diff --git a/addons/event_sale/tests/test_event_sale.py b/addons/event_sale/tests/test_event_sale.py
index 4fd177dc438..e47a45bbe3f 100644
--- a/addons/event_sale/tests/test_event_sale.py
+++ b/addons/event_sale/tests/test_event_sale.py
@@ -73,6 +73,39 @@ class TestEventSale(TestEventSaleCommon):
             {'name': 'Test Account Tax Group', 'company_id': cls.env.company.id}
         )
 
+    @users('user_sales_salesman')
+    def test_adjusted_quantity_in_sale_order(self):
+        """ This test ensures that when reducing the quantity of tickets for an event, we will cancel the
+        registrations for those tickets too.
+        """
+        customer_so = self.customer_so.with_user(self.env.user)
+        ticket = self.event_0.event_ticket_ids[0]
+
+        customer_so.write({
+            'order_line': [
+                (0, 0, {
+                    'event_id': self.event_0.id,
+                    'event_ticket_id': ticket.id,
+                    'product_id': ticket.product_id.id,
+                    'product_uom_qty': 3,
+                    'price_unit': 10,
+                })
+            ]
+        })
+
+        editor = self.env['registration.editor'].with_context({'default_sale_order_id': customer_so.id}).create({})
+        editor.action_make_registration()
+
+        registration_to_cancel = self.event_0.registration_ids[0]
+        registration_to_cancel.action_cancel()
+
+        registrations = self.env['event.registration'].search([('sale_order_id', '=', customer_so.id)])
+
+        expected_states = ['draft', 'draft', 'cancel']
+        actual_states = registrations.sorted('id').mapped('state')
+
+        self.assertListEqual(actual_states, expected_states, "One of the registrations should be cancelled.")
+
     @users('user_sales_salesman')
     def test_event_crm_sale(self):
         TICKET1_COUNT, TICKET2_COUNT = 3, 1