diff --git a/azure/durable_functions/models/Task.py b/azure/durable_functions/models/Task.py
index e5667001..447ee540 100644
--- a/azure/durable_functions/models/Task.py
+++ b/azure/durable_functions/models/Task.py
@@ -380,6 +380,8 @@ def cancel(self):
         if (self.result):
             raise Exception("Cannot cancel a completed task.")
         self.action.is_cancelled = True
+        for timer in self.pending_tasks:
+            timer.cancel()
 
     def try_set_value(self, child: TimerTask):
         """Transition this LongTimer Task to a terminal state and set its value.
@@ -394,7 +396,7 @@ def try_set_value(self, child: TimerTask):
         """
         current_time = self._orchestration_context.current_utc_datetime
         final_fire_time = self.action.fire_at
-        if final_fire_time > current_time:
+        if not self.is_canceled() and final_fire_time > current_time:
             next_timer = self.get_next_timer_task(final_fire_time, current_time)
             self.add_new_child(next_timer)
         return super().try_set_value(child)
diff --git a/tests/tasks/test_long_timers.py b/tests/tasks/test_long_timers.py
index e3dceb23..4f16379f 100644
--- a/tests/tasks/test_long_timers.py
+++ b/tests/tasks/test_long_timers.py
@@ -1,9 +1,13 @@
 import datetime
+import json
 
 import pytest
 from azure.durable_functions.models.DurableOrchestrationContext import DurableOrchestrationContext
 from azure.durable_functions.models.Task import LongTimerTask, TaskState, TimerTask
 from azure.durable_functions.models.actions.CreateTimerAction import CreateTimerAction
+from azure.durable_functions.models.ReplaySchema import ReplaySchema
+from azure.durable_functions.orchestrator import Orchestrator
+from tests.test_utils.ContextBuilder import ContextBuilder
 
 
 @pytest.fixture
@@ -68,3 +72,81 @@ def test_long_timer_fires_appropriately(starting_context_v3):
     # Ensure the LongTimerTask finished
     assert len(long_timer.pending_tasks) == 0
     assert long_timer.state == TaskState.SUCCEEDED
+
+
+@pytest.mark.parametrize("completed_chunk", [False, True])
+def test_cancel_long_timer_cancels_pending_chunk(starting_context_v3, completed_chunk):
+    context = starting_context_v3
+    timer = context.create_timer(context.current_utc_datetime + datetime.timedelta(days=2))
+    first_chunk = next(iter(timer.pending_tasks))
+    if completed_chunk:
+        context.current_utc_datetime = first_chunk.action_repr.fire_at
+        first_chunk.set_value(False, None)
+
+    pending_chunk = next(iter(timer.pending_tasks))
+    timer.cancel()
+    timer.cancel()  # Like short timers, cancellation is idempotent before completion.
+
+    assert timer.is_canceled()
+    assert pending_chunk.is_cancelled
+    if completed_chunk:
+        assert not first_chunk.is_cancelled
+
+
+@pytest.mark.parametrize("completed_chunk", [False, True])
+def test_approval_cancels_serialized_long_timer(completed_chunk):
+    def approval(context):
+        event = context.wait_for_external_event("approved")
+        timer = context.create_timer(context.current_utc_datetime + datetime.timedelta(days=2))
+        winner = yield context.task_any([event, timer])
+        if winner == event:
+            timer.cancel()
+            return True
+        return False
+
+    builder = ContextBuilder("approval", increase_time=False, replay_schema=ReplaySchema.V3)
+    first_fire = builder.current_datetime + datetime.timedelta(hours=8)
+    builder.add_timer_created_event(0, first_fire.isoformat())
+    builder.add_orchestrator_completed_event()
+    if completed_chunk:
+        builder.current_datetime = first_fire
+        builder.add_orchestrator_started_event()
+        builder.add_timer_fired_event(0, first_fire.isoformat())
+        second_fire = first_fire + datetime.timedelta(hours=8)
+        builder.add_timer_created_event(1, second_fire.isoformat())
+        builder.add_orchestrator_completed_event()
+    builder.add_orchestrator_started_event()
+    builder.add_event_raised_event("approved", -1, "true")
+    context = DurableOrchestrationContext.from_json(builder.to_json_string(
+        maximumShortTimerDuration="0.16:00:00",
+        longRunningTimerIntervalDuration="0.08:00:00"))
+
+    result = json.loads(Orchestrator(approval).handle(context))
+    assert result["isDone"]
+    assert result["output"] is True
+
+    def timer_actions(actions):
+        for action in actions:
+            if "isCanceled" in action:
+                yield action
+            yield from timer_actions(action.get("compoundActions", []))
+
+    timers = list(timer_actions([action for group in result["actions"] for action in group]))
+    assert len(timers) == (2 if completed_chunk else 1)
+    assert timers[-1]["isCanceled"]
+    if completed_chunk:
+        assert not timers[0]["isCanceled"]
+
+
+def test_cancelled_long_timer_does_not_schedule_another_chunk(starting_context_v3):
+    context = starting_context_v3
+    timer = context.create_timer(context.current_utc_datetime + datetime.timedelta(days=2))
+    chunk = next(iter(timer.pending_tasks))
+    timer.cancel()
+
+    # A firing already in history must not restart the cancelled timer.
+    context.current_utc_datetime = chunk.action_repr.fire_at
+    chunk.set_value(False, None)
+
+    assert not timer.pending_tasks
+    assert not any(context._actions)