diff --git a/amber/src/main/python/core/util/customized_queue/linked_blocking_multi_queue.py b/amber/src/main/python/core/util/customized_queue/linked_blocking_multi_queue.py
index fcf175d6bcd..629fe92d6c6 100644
--- a/amber/src/main/python/core/util/customized_queue/linked_blocking_multi_queue.py
+++ b/amber/src/main/python/core/util/customized_queue/linked_blocking_multi_queue.py
@@ -421,9 +421,12 @@ def add_sub_queue(self, key: K, priority: int) -> Optional[SubQueue]:
                         added = True
                         break
                     elif pg.priority > priority:
+                        # pg has a lower priority than the new group, so the new
+                        # group belongs in front of it: priority_groups must stay
+                        # sorted because the selection strategy walks it in order.
                         new_pg = self.PriorityGroup(priority)
                         new_pg.add_queue(sub_queue)
-                        self.priority_groups.append(new_pg)
+                        self.priority_groups.insert(i, new_pg)
                         added = True
                         break
 
diff --git a/amber/src/test/python/core/models/test_internal_queue.py b/amber/src/test/python/core/models/test_internal_queue.py
index 663f95d89a8..50797f69c2d 100644
--- a/amber/src/test/python/core/models/test_internal_queue.py
+++ b/amber/src/test/python/core/models/test_internal_queue.py
@@ -116,13 +116,6 @@ def test_it_accepts_all_recognized_element_types(
         assert queue.is_empty()
 
     @pytest.mark.timeout(2)
-    @pytest.mark.xfail(
-        reason=(
-            "LinkedBlockingMultiQueue.add_sub_queue does not currently insert new "
-            "priority groups ahead of lower-priority ones, so registering data before "
-            "control can break control-priority ordering."
-        )
-    )
     def test_control_elements_dequeue_before_data_even_if_data_channel_registered_first(
         self, queue, control_channel, data_channel
     ):