diff --git a/airflow/www/views.py b/airflow/www/views.py
index 951ed496da646..ed20bc16572f3 100644
--- a/airflow/www/views.py
+++ b/airflow/www/views.py
@@ -3236,10 +3236,12 @@ def duration(self, dag_id: str, session: Session = NEW_SESSION):
             if failed_task_instance.duration:
                 fails_totals[dict_key] += failed_task_instance.duration
 
-        # we must group any mapped TIs by dag_id, task_id, run_id
+        # We must group any mapped TIs by dag_id, task_id, run_id
+        def grouping_key(ti: TaskInstance):
+            return ti.dag_id, ti.task_id, ti.run_id
+
         mapped_tis = set()
-        tis_grouped = itertools.groupby(task_instances, lambda x: (x.dag_id, x.task_id, x.run_id))
-        for _, group in tis_grouped:
+        for _, group in itertools.groupby(sorted(task_instances, key=grouping_key), key=grouping_key):
             tis = list(group)
             duration = sum(x.duration for x in tis if x.duration)
             if duration: