diff --git a/packages/durabletask-js/src/worker/runtime-orchestration-context.ts b/packages/durabletask-js/src/worker/runtime-orchestration-context.ts
index 7d77dd3..157e036 100644
--- a/packages/durabletask-js/src/worker/runtime-orchestration-context.ts
+++ b/packages/durabletask-js/src/worker/runtime-orchestration-context.ts
@@ -48,7 +48,7 @@ export class RuntimeOrchestrationContext extends OrchestrationContext {
   _pendingEvents: Record<string, CompletableTask<any>[]>;
   _newInput?: any;
   _saveEvents: boolean;
-  _customStatus?: any;
+  _customStatus?: string;
   _entityFeature: RuntimeOrchestrationEntityFeature;
 
   constructor(instanceId: string) {
@@ -402,20 +402,35 @@ export class RuntimeOrchestrationContext extends OrchestrationContext {
 
   /**
    * Sets a custom status value for the current orchestration instance.
+   *
+   * The value is serialized eagerly via JSON.stringify so that serialization
+   * errors surface inside the orchestrator execution (where they are caught
+   * by the executor's try-catch) rather than after execution completes.
    */
   setCustomStatus(customStatus: any): void {
-    this._customStatus = customStatus;
+    if (customStatus === undefined || customStatus === null) {
+      this._customStatus = undefined;
+      return;
+    }
+
+    try {
+      this._customStatus = JSON.stringify(customStatus);
+    } catch (e) {
+      throw new Error(
+        `Custom status value is not JSON-serializable: ${e instanceof Error ? e.message : String(e)}`,
+        { cause: e },
+      );
+    }
   }
 
   /**
    * Gets the encoded custom status value for the current orchestration instance.
    * This is used internally when building the orchestrator response.
+   *
+   * Returns the pre-serialized JSON string set by setCustomStatus().
    */
   getCustomStatus(): string | undefined {
-    if (this._customStatus === undefined || this._customStatus === null) {
-      return undefined;
-    }
-    return JSON.stringify(this._customStatus);
+    return this._customStatus;
   }
 
   /**
diff --git a/packages/durabletask-js/test/orchestration_context_methods.spec.ts b/packages/durabletask-js/test/orchestration_context_methods.spec.ts
index 9eea1f5..e878e38 100644
--- a/packages/durabletask-js/test/orchestration_context_methods.spec.ts
+++ b/packages/durabletask-js/test/orchestration_context_methods.spec.ts
@@ -151,6 +151,106 @@ describe("OrchestrationContext.setCustomStatus", () => {
     // The last set value should be returned
     expect(result.customStatus).toEqual('"step3"');
   });
+
+  it("should fail the orchestration when custom status contains a circular reference", async () => {
+    const circular: Record<string, unknown> = { key: "value" };
+    circular.self = circular;
+
+    const orchestrator: TOrchestrator = async (ctx: OrchestrationContext) => {
+      ctx.setCustomStatus(circular);
+      return "done";
+    };
+
+    const registry = new Registry();
+    const name = registry.addOrchestrator(orchestrator);
+    const newEvents = [
+      newOrchestratorStartedEvent(),
+      newExecutionStartedEvent(name, TEST_INSTANCE_ID),
+    ];
+    const executor = new OrchestrationExecutor(registry);
+    const result = await executor.execute(TEST_INSTANCE_ID, [], newEvents);
+
+    // The orchestration should fail gracefully instead of crashing the executor
+    const completeAction = result.actions.find((a) => a.getCompleteorchestration());
+    expect(completeAction).toBeDefined();
+    expect(completeAction?.getCompleteorchestration()?.getOrchestrationstatus()).toEqual(
+      pb.OrchestrationStatus.ORCHESTRATION_STATUS_FAILED,
+    );
+    const failureDetails = completeAction?.getCompleteorchestration()?.getFailuredetails();
+    expect(failureDetails?.getErrormessage()).toContain("not JSON-serializable");
+  });
+
+  it("should fail the orchestration when custom status contains a BigInt", async () => {
+    const orchestrator: TOrchestrator = async (ctx: OrchestrationContext) => {
+      ctx.setCustomStatus({ count: BigInt(42) });
+      return "done";
+    };
+
+    const registry = new Registry();
+    const name = registry.addOrchestrator(orchestrator);
+    const newEvents = [
+      newOrchestratorStartedEvent(),
+      newExecutionStartedEvent(name, TEST_INSTANCE_ID),
+    ];
+    const executor = new OrchestrationExecutor(registry);
+    const result = await executor.execute(TEST_INSTANCE_ID, [], newEvents);
+
+    // The orchestration should fail gracefully instead of crashing the executor
+    const completeAction = result.actions.find((a) => a.getCompleteorchestration());
+    expect(completeAction).toBeDefined();
+    expect(completeAction?.getCompleteorchestration()?.getOrchestrationstatus()).toEqual(
+      pb.OrchestrationStatus.ORCHESTRATION_STATUS_FAILED,
+    );
+    const failureDetails = completeAction?.getCompleteorchestration()?.getFailuredetails();
+    expect(failureDetails?.getErrormessage()).toContain("not JSON-serializable");
+  });
+
+  it("should allow clearing custom status by setting it to null", async () => {
+    const orchestrator: TOrchestrator = async (ctx: OrchestrationContext) => {
+      ctx.setCustomStatus("initial");
+      ctx.setCustomStatus(null);
+      return "done";
+    };
+
+    const registry = new Registry();
+    const name = registry.addOrchestrator(orchestrator);
+    const newEvents = [
+      newOrchestratorStartedEvent(),
+      newExecutionStartedEvent(name, TEST_INSTANCE_ID),
+    ];
+    const executor = new OrchestrationExecutor(registry);
+    const result = await executor.execute(TEST_INSTANCE_ID, [], newEvents);
+
+    expect(result.customStatus).toBeUndefined();
+  });
+
+  it("should preserve orchestration result when non-serializable status is set after a valid one", async () => {
+    const circular: Record<string, unknown> = { key: "value" };
+    circular.self = circular;
+
+    const orchestrator: TOrchestrator = async (ctx: OrchestrationContext) => {
+      ctx.setCustomStatus("good status");
+      ctx.setCustomStatus(circular); // This should throw
+      return "done";
+    };
+
+    const registry = new Registry();
+    const name = registry.addOrchestrator(orchestrator);
+    const newEvents = [
+      newOrchestratorStartedEvent(),
+      newExecutionStartedEvent(name, TEST_INSTANCE_ID),
+    ];
+    const executor = new OrchestrationExecutor(registry);
+    const result = await executor.execute(TEST_INSTANCE_ID, [], newEvents);
+
+    // The orchestration should fail (not crash) — the serialization error
+    // is thrown inside orchestrator code and caught by the executor
+    const completeAction = result.actions.find((a) => a.getCompleteorchestration());
+    expect(completeAction).toBeDefined();
+    expect(completeAction?.getCompleteorchestration()?.getOrchestrationstatus()).toEqual(
+      pb.OrchestrationStatus.ORCHESTRATION_STATUS_FAILED,
+    );
+  });
 });
 
 describe("OrchestrationContext.sendEvent", () => {