diff --git a/packages/durabletask-js/src/worker/orchestration-executor.ts b/packages/durabletask-js/src/worker/orchestration-executor.ts
index 789d3e1..3d17d76 100644
--- a/packages/durabletask-js/src/worker/orchestration-executor.ts
+++ b/packages/durabletask-js/src/worker/orchestration-executor.ts
@@ -386,25 +386,11 @@ export class OrchestrationExecutor {
   }
 
   private async handleSubOrchestrationCompleted(ctx: RuntimeOrchestrationContext, event: pb.HistoryEvent): Promise<void> {
-    const subOrchestrationInstanceCompletedEvent = event.getSuborchestrationinstancecompleted();
-    const taskId = subOrchestrationInstanceCompletedEvent
-      ? subOrchestrationInstanceCompletedEvent.getTaskscheduledid()
-      : undefined;
-
-    let subOrchTask;
-
-    if (taskId !== undefined) {
-      subOrchTask = ctx._pendingTasks[taskId];
-      delete ctx._pendingTasks[taskId];
-    }
-
-    const result = parseJsonField(subOrchestrationInstanceCompletedEvent?.getResult());
-
-    if (subOrchTask) {
-      subOrchTask.complete(result);
-    }
-
-    await ctx.resume();
+    const completedEvent = event.getSuborchestrationinstancecompleted();
+    const taskId = completedEvent ? completedEvent.getTaskscheduledid() : undefined;
+    const result = completedEvent?.getResult();
+    const normalizedResult = isEmpty(result) ? undefined : result;
+    await this.handleCompletedTask(ctx, taskId, normalizedResult, "subOrchestrationInstanceCompleted");
   }
 
   private async handleSubOrchestrationFailed(ctx: RuntimeOrchestrationContext, event: pb.HistoryEvent): Promise<void> {
diff --git a/packages/durabletask-js/test/orchestration_executor.spec.ts b/packages/durabletask-js/test/orchestration_executor.spec.ts
index 2783750..f1f0dba 100644
--- a/packages/durabletask-js/test/orchestration_executor.spec.ts
+++ b/packages/durabletask-js/test/orchestration_executor.spec.ts
@@ -23,7 +23,8 @@ import { OrchestrationExecutor, OrchestrationExecutionResult } from "../src/work
 import * as pb from "../src/proto/orchestrator_service_pb";
 import { Registry } from "../src/worker/registry";
 import { TOrchestrator } from "../src/types/orchestrator.type";
-import { NoOpLogger } from "../src/types/logger.type";
+import { NoOpLogger, StructuredLogger, LogEvent } from "../src/types/logger.type";
+import { EVENT_ORCHESTRATION_UNEXPECTED_EVENT } from "../src/worker/logs";
 import { ActivityContext } from "../src/task/context/activity-context";
 import { CompletableTask } from "../src/task/completable-task";
 import { Task } from "../src/task/task";
@@ -570,6 +571,52 @@ describe("Orchestration Executor", () => {
     // assert user_code_statement in complete_action.failureDetails.stackTrace.value
   });
 
+  it("should produce no actions and log a warning when sub-orchestration completion has unmatched taskId", async () => {
+    const subOrchestrator = async (_: OrchestrationContext) => {
+      // do nothing
+    };
+    const orchestrator: TOrchestrator = async function* (ctx: OrchestrationContext, _: any): any {
+      const res = yield ctx.callSubOrchestrator(subOrchestrator);
+      return res;
+    };
+    const registry = new Registry();
+    const subOrchestratorName = registry.addOrchestrator(subOrchestrator);
+    const orchestratorName = registry.addOrchestrator(orchestrator);
+    const oldEvents = [
+      newOrchestratorStartedEvent(),
+      newExecutionStartedEvent(orchestratorName, TEST_INSTANCE_ID, undefined),
+      newSubOrchestrationCreatedEvent(1, subOrchestratorName, "sub-orch-123"),
+    ];
+    // Send a completion event with a taskId (999) that does not match any pending task.
+    const newEvents = [newSubOrchestrationCompletedEvent(999, JSON.stringify("unexpected"))];
+
+    // Use a spy logger to verify the warning log is emitted via handleCompletedTask's guard clause
+    const loggedEvents: LogEvent[] = [];
+    const spyLogger: StructuredLogger = {
+      error: () => {},
+      warn: () => {},
+      info: () => {},
+      debug: () => {},
+      logEvent: (_level, event, _message) => {
+        loggedEvents.push(event);
+      },
+    };
+
+    const executor = new OrchestrationExecutor(registry, spyLogger);
+    const result = await executor.execute(TEST_INSTANCE_ID, oldEvents, newEvents);
+
+    // The orchestration should still be waiting for the real sub-orchestration to complete.
+    expect(result.actions.length).toEqual(0);
+
+    // Verify the unexpected event warning was logged (proves the guard clause was hit)
+    const unexpectedEvents = loggedEvents.filter(
+      (e) => e.eventId === EVENT_ORCHESTRATION_UNEXPECTED_EVENT,
+    );
+    expect(unexpectedEvents.length).toEqual(1);
+    expect(unexpectedEvents[0].properties?.eventType).toEqual("subOrchestrationInstanceCompleted");
+    expect(unexpectedEvents[0].properties?.eventId).toEqual(999);
+  });
+
   it("should test that an orchestration can wait for and process an external event sent by a client", async () => {
     const orchestrator: TOrchestrator = async function* (ctx: OrchestrationContext, _: any): any {
       const res = yield ctx.waitForExternalEvent("my_event");