diff --git a/airflow-core/tests/unit/models/test_taskinstance.py b/airflow-core/tests/unit/models/test_taskinstance.py
index b9e5452855ff1..c2bf05cd2036b 100644
--- a/airflow-core/tests/unit/models/test_taskinstance.py
+++ b/airflow-core/tests/unit/models/test_taskinstance.py
@@ -19,6 +19,7 @@
 
 import contextlib
 import datetime
+import json
 import operator
 import os
 import pathlib
@@ -2873,6 +2874,30 @@ def test_defer_task(create_task_instance):
     assert ti.trigger_timeout is None
 
 
+def test_defer_task_serializes_non_json_next_kwargs(create_task_instance):
+    from airflow.sdk.serde import deserialize
+    from airflow.triggers.base import StartTriggerArgs
+
+    session = mock.Mock(spec=["add", "flush"])
+    delay = datetime.timedelta(minutes=5)
+    start_at = timezone.utcnow()
+    ti = create_task_instance(
+        dag_id="test_defer_task_serializes_non_json_next_kwargs",
+        task_id="test_defer_task_serializes_non_json_next_kwargs_op",
+        start_from_trigger=True,
+        start_trigger_args=StartTriggerArgs(
+            trigger_cls="trigger_cls",
+            next_method="next_method",
+            trigger_kwargs={"key": "value"},
+            next_kwargs={"start_at": start_at, "delay": delay},
+        ),
+    )
+
+    assert ti.defer_task(session=session)
+    json.dumps(ti.next_kwargs)
+    assert deserialize(ti.next_kwargs) == {"start_at": start_at, "delay": delay}
+
+
 def test_defer_task_with_trigger_timeout(create_task_instance):
     from airflow.models.trigger import Trigger
     from airflow.triggers.base import StartTriggerArgs