diff --git a/packages/durabletask-js/src/testing/in-memory-backend.ts b/packages/durabletask-js/src/testing/in-memory-backend.ts
index 2c96acb..64f6824 100644
--- a/packages/durabletask-js/src/testing/in-memory-backend.ts
+++ b/packages/durabletask-js/src/testing/in-memory-backend.ts
@@ -62,6 +62,7 @@ export class InMemoryOrchestrationBackend {
   private readonly activityQueue: ActivityWorkItem[] = [];
   private readonly stateWaiters: Map<string, StateWaiter[]> = new Map();
   private readonly pendingTimers: Set<ReturnType<typeof setTimeout>> = new Set();
+  private readonly instanceTimers: Map<string, Set<ReturnType<typeof setTimeout>>> = new Map();
   private nextCompletionToken: number = 1;
   private readonly maxHistorySize: number;
 
@@ -217,6 +218,7 @@ export class InMemoryOrchestrationBackend {
 
     this.instances.delete(instanceId);
     this.stateWaiters.delete(instanceId);
+    this.cancelInstanceTimers(instanceId);
     return true;
   }
 
@@ -394,6 +396,7 @@ export class InMemoryOrchestrationBackend {
       clearTimeout(timer);
     }
     this.pendingTimers.clear();
+    this.instanceTimers.clear();
   }
 
   /**
@@ -543,6 +546,7 @@ export class InMemoryOrchestrationBackend {
 
     const timerHandle = setTimeout(() => {
       this.pendingTimers.delete(timerHandle);
+      this.removeInstanceTimer(instance.instanceId, timerHandle);
       const currentInstance = this.instances.get(instance.instanceId);
       if (currentInstance && !this.isTerminalStatus(currentInstance.status)) {
         const timerFiredEvent = pbh.newTimerFiredEvent(timerId, fireAt);
@@ -552,6 +556,7 @@ export class InMemoryOrchestrationBackend {
       }
     }, delay);
     this.pendingTimers.add(timerHandle);
+    this.addInstanceTimer(instance.instanceId, timerHandle);
   }
 
   private processCreateSubOrchestrationAction(instance: OrchestrationInstance, action: pb.OrchestratorAction): void {
@@ -638,6 +643,36 @@ export class InMemoryOrchestrationBackend {
     }
   }
 
+  private addInstanceTimer(instanceId: string, timerHandle: ReturnType<typeof setTimeout>): void {
+    let timers = this.instanceTimers.get(instanceId);
+    if (!timers) {
+      timers = new Set();
+      this.instanceTimers.set(instanceId, timers);
+    }
+    timers.add(timerHandle);
+  }
+
+  private removeInstanceTimer(instanceId: string, timerHandle: ReturnType<typeof setTimeout>): void {
+    const timers = this.instanceTimers.get(instanceId);
+    if (timers) {
+      timers.delete(timerHandle);
+      if (timers.size === 0) {
+        this.instanceTimers.delete(instanceId);
+      }
+    }
+  }
+
+  private cancelInstanceTimers(instanceId: string): void {
+    const timers = this.instanceTimers.get(instanceId);
+    if (timers) {
+      for (const timer of timers) {
+        clearTimeout(timer);
+        this.pendingTimers.delete(timer);
+      }
+      this.instanceTimers.delete(instanceId);
+    }
+  }
+
   private notifyWaiters(instanceId: string): void {
     const instance = this.instances.get(instanceId);
     const waiters = this.stateWaiters.get(instanceId);
diff --git a/packages/durabletask-js/test/in-memory-backend.spec.ts b/packages/durabletask-js/test/in-memory-backend.spec.ts
index 66fe6a9..a4d6d3b 100644
--- a/packages/durabletask-js/test/in-memory-backend.spec.ts
+++ b/packages/durabletask-js/test/in-memory-backend.spec.ts
@@ -356,6 +356,73 @@ describe("In-Memory Backend", () => {
     expect(state).toBeUndefined();
   });
 
+  it("should cancel pending timers when purging a terminated orchestration", async () => {
+    const orchestrator: TOrchestrator = async function* (ctx: OrchestrationContext): any {
+      // Create a timer far in the future — it will still be pending when we terminate
+      yield ctx.createTimer(3600);
+      return "done";
+    };
+
+    worker.addOrchestrator(orchestrator);
+    await worker.start();
+
+    const id = await client.scheduleNewOrchestration(orchestrator);
+    // Wait for the orchestration to start so the timer action is processed by the backend
+    await client.waitForOrchestrationStart(id, false, 5);
+
+    // Terminate while the long timer is still pending
+    await client.terminateOrchestration(id, "terminated");
+    const state = await client.waitForOrchestrationCompletion(id, true, 10);
+    expect(state?.runtimeStatus).toEqual(OrchestrationStatus.TERMINATED);
+
+    // Timer should still be pending before purge
+    const pendingTimersBefore = (backend as any).pendingTimers.size;
+    expect(pendingTimersBefore).toBeGreaterThan(0);
+
+    // Purge the terminated orchestration
+    const result = await client.purgeOrchestration(id);
+    expect(result.deletedInstanceCount).toEqual(1);
+
+    // After purge, pending timers for this instance should be cancelled
+    expect((backend as any).pendingTimers.size).toBe(0);
+    expect((backend as any).instanceTimers.size).toBe(0);
+  });
+
+  it("should cancel pending timers for only the purged orchestration", async () => {
+    const timerOrchestrator: TOrchestrator = async function* (ctx: OrchestrationContext): any {
+      yield ctx.createTimer(3600);
+      return "done";
+    };
+
+    const waitOrchestrator: TOrchestrator = async function* (ctx: OrchestrationContext): any {
+      yield ctx.createTimer(7200);
+      return "done";
+    };
+
+    worker.addOrchestrator(timerOrchestrator);
+    worker.addOrchestrator(waitOrchestrator);
+    await worker.start();
+
+    // Start two orchestrations that both create long timers
+    const id1 = await client.scheduleNewOrchestration(timerOrchestrator);
+    const id2 = await client.scheduleNewOrchestration(waitOrchestrator);
+
+    await client.waitForOrchestrationStart(id1, false, 5);
+    await client.waitForOrchestrationStart(id2, false, 5);
+
+    // Terminate and purge only the first orchestration
+    await client.terminateOrchestration(id1, "terminated");
+    await client.waitForOrchestrationCompletion(id1, false, 10);
+
+    const result = await client.purgeOrchestration(id1);
+    expect(result.deletedInstanceCount).toEqual(1);
+
+    // The second orchestration's timer should still be pending
+    expect((backend as any).pendingTimers.size).toBe(1);
+    expect((backend as any).instanceTimers.has(id2)).toBe(true);
+    expect((backend as any).instanceTimers.has(id1)).toBe(false);
+  });
+
   it("should allow reusing instance IDs after reset", async () => {
     const orchestrator: TOrchestrator = async (_: OrchestrationContext, input: number) => {
       return input * 2;