diff --git a/packages/durabletask-js/src/worker/orchestration-executor.ts b/packages/durabletask-js/src/worker/orchestration-executor.ts
index c5eea00..ac21732 100644
--- a/packages/durabletask-js/src/worker/orchestration-executor.ts
+++ b/packages/durabletask-js/src/worker/orchestration-executor.ts
@@ -792,16 +792,20 @@ export class OrchestrationExecutor {
       task.recordFailure(errorMessage, failureDetails);
       const retryResult = await task.shouldRetry(ctx._currentUtcDatetime);
 
-      if (retryResult !== false) {
+      // Only retry when the handler explicitly returns true or a finite number.
+      // Using a positive check (=== true || finite number) instead of !== false
+      // ensures that undefined/null (e.g., from a missing return statement) is
+      // treated as "don't retry" rather than causing an infinite retry loop.
+      if (retryResult === true || (typeof retryResult === "number" && Number.isFinite(retryResult))) {
         WorkerLogs.retryingTask(this._logger, ctx._instanceId, task.taskName, task.attemptCount);
         task.incrementAttemptCount();
 
         if (typeof retryResult === "number") {
           if (retryResult <= 0) {
-            // Handler returned true — retry immediately
+            // Zero or negative delay — retry immediately
             ctx.rescheduleRetryTask(task);
           } else {
-            // Handler returned a delay in milliseconds — use a timer
+            // Positive delay in milliseconds — use a timer
             ctx.createRetryTimer(task, retryResult);
           }
         } else {
diff --git a/packages/durabletask-js/test/orchestration_executor.spec.ts b/packages/durabletask-js/test/orchestration_executor.spec.ts
index 7b2795e..fb8200d 100644
--- a/packages/durabletask-js/test/orchestration_executor.spec.ts
+++ b/packages/durabletask-js/test/orchestration_executor.spec.ts
@@ -1127,6 +1127,135 @@ describe("Orchestration Executor", () => {
       const completeAction = getAndValidateSingleCompleteOrchestrationAction(result);
       expect(completeAction?.getOrchestrationstatus()).toEqual(pb.OrchestrationStatus.ORCHESTRATION_STATUS_FAILED);
     });
+
+    it("should fail the task (not retry) when retry handler returns undefined", async () => {
+      const { result: startResult, replay } = await startOrchestration(
+        async function* (ctx: OrchestrationContext): any {
+          // Cast to bypass TypeScript — simulates a JavaScript consumer or a handler
+          // with a code path that omits a return statement
+          const retryHandler = (async (_retryCtx: any) => {
+            // Intentionally missing return statement
+          }) as any;
+          return yield ctx.callActivity("flakyActivity", undefined, { retry: retryHandler });
+        },
+      );
+
+      expect(startResult.actions[0].hasScheduletask()).toBe(true);
+
+      // Activity fails → handler returns undefined → should NOT retry, task should fail
+      const result = await replay(
+        [newTaskScheduledEvent(1, "flakyActivity")],
+        [newTaskFailedEvent(1, new Error("Activity error"))],
+      );
+      const completeAction = getAndValidateSingleCompleteOrchestrationAction(result);
+      expect(completeAction?.getOrchestrationstatus()).toEqual(pb.OrchestrationStatus.ORCHESTRATION_STATUS_FAILED);
+    });
+
+    it("should fail the task (not retry) when retry handler returns null", async () => {
+      const { result: startResult, replay } = await startOrchestration(
+        async function* (ctx: OrchestrationContext): any {
+          const retryHandler = async (_retryCtx: any) => {
+            return null as any;
+          };
+          return yield ctx.callActivity("flakyActivity", undefined, { retry: retryHandler });
+        },
+      );
+
+      expect(startResult.actions[0].hasScheduletask()).toBe(true);
+
+      // Activity fails → handler returns null → should NOT retry, task should fail
+      const result = await replay(
+        [newTaskScheduledEvent(1, "flakyActivity")],
+        [newTaskFailedEvent(1, new Error("Activity error"))],
+      );
+      const completeAction = getAndValidateSingleCompleteOrchestrationAction(result);
+      expect(completeAction?.getOrchestrationstatus()).toEqual(pb.OrchestrationStatus.ORCHESTRATION_STATUS_FAILED);
+    });
+
+    it("should create a retry timer when retry handler returns a positive delay", async () => {
+      const { result: startResult, replay } = await startOrchestration(
+        async function* (ctx: OrchestrationContext): any {
+          const retryHandler = async (_retryCtx: any) => {
+            return 5000; // Retry after 5 seconds
+          };
+          return yield ctx.callActivity("flakyActivity", undefined, { retry: retryHandler });
+        },
+      );
+
+      expect(startResult.actions[0].hasScheduletask()).toBe(true);
+
+      // Activity fails → handler returns 5000 → should create a timer
+      const result = await replay(
+        [newTaskScheduledEvent(1, "flakyActivity")],
+        [newTaskFailedEvent(1, new Error("Transient failure"))],
+      );
+      expect(result.actions.length).toBe(1);
+      expect(result.actions[0].hasCreatetimer()).toBe(true);
+    });
+
+    it("should retry immediately when retry handler returns 0", async () => {
+      const { result: startResult, replay } = await startOrchestration(
+        async function* (ctx: OrchestrationContext): any {
+          const retryHandler = async (_retryCtx: any) => {
+            return 0; // Retry immediately via zero delay
+          };
+          return yield ctx.callActivity("flakyActivity", undefined, { retry: retryHandler });
+        },
+      );
+
+      expect(startResult.actions[0].hasScheduletask()).toBe(true);
+
+      // Activity fails → handler returns 0 → should reschedule immediately (no timer)
+      const result = await replay(
+        [newTaskScheduledEvent(1, "flakyActivity")],
+        [newTaskFailedEvent(1, new Error("Transient failure"))],
+      );
+      expect(result.actions.length).toBe(1);
+      expect(result.actions[0].hasScheduletask()).toBe(true);
+      expect(result.actions[0].getScheduletask()?.getName()).toBe("flakyActivity");
+    });
+
+    it("should fail the task when retry handler returns NaN", async () => {
+      const { result: startResult, replay } = await startOrchestration(
+        async function* (ctx: OrchestrationContext): any {
+          const retryHandler = async (_retryCtx: any) => {
+            return NaN;
+          };
+          return yield ctx.callActivity("flakyActivity", undefined, { retry: retryHandler });
+        },
+      );
+
+      expect(startResult.actions[0].hasScheduletask()).toBe(true);
+
+      // Activity fails → handler returns NaN → should NOT retry
+      const result = await replay(
+        [newTaskScheduledEvent(1, "flakyActivity")],
+        [newTaskFailedEvent(1, new Error("Activity error"))],
+      );
+      const completeAction = getAndValidateSingleCompleteOrchestrationAction(result);
+      expect(completeAction?.getOrchestrationstatus()).toEqual(pb.OrchestrationStatus.ORCHESTRATION_STATUS_FAILED);
+    });
+
+    it("should fail the task when retry handler returns Infinity", async () => {
+      const { result: startResult, replay } = await startOrchestration(
+        async function* (ctx: OrchestrationContext): any {
+          const retryHandler = async (_retryCtx: any) => {
+            return Infinity;
+          };
+          return yield ctx.callActivity("flakyActivity", undefined, { retry: retryHandler });
+        },
+      );
+
+      expect(startResult.actions[0].hasScheduletask()).toBe(true);
+
+      // Activity fails → handler returns Infinity → should NOT retry
+      const result = await replay(
+        [newTaskScheduledEvent(1, "flakyActivity")],
+        [newTaskFailedEvent(1, new Error("Activity error"))],
+      );
+      const completeAction = getAndValidateSingleCompleteOrchestrationAction(result);
+      expect(completeAction?.getOrchestrationstatus()).toEqual(pb.OrchestrationStatus.ORCHESTRATION_STATUS_FAILED);
+    });
   });
 
   it("should complete immediately when whenAll is called with an empty task array", async () => {
diff --git a/test/e2e-azuremanaged/orchestration.spec.ts b/test/e2e-azuremanaged/orchestration.spec.ts
index 47792a2..cee61b7 100644
--- a/test/e2e-azuremanaged/orchestration.spec.ts
+++ b/test/e2e-azuremanaged/orchestration.spec.ts
@@ -657,6 +657,144 @@ describe("Durable Task Scheduler (DTS) E2E Tests", () => {
     expect(invoked).toBe(true);
   }, 31000);
 
+  // ==================== Retry Handler Tests ====================
+
+  it("should fail (not retry infinitely) when retry handler returns undefined", async () => {
+    // Issue: A retry handler with a missing return statement returns undefined.
+    // Before the fix, `undefined !== false` was truthy, so the executor treated it
+    // as "retry", causing an infinite retry loop. The fix uses a positive check:
+    // only `true` or a finite number triggers a retry.
+    let attemptCount = 0;
+
+    const failingActivity = async (_: ActivityContext) => {
+      attemptCount++;
+      throw new Error(`Failure on attempt ${attemptCount}`);
+    };
+
+    const orchestrator: TOrchestrator = async function* (ctx: OrchestrationContext): any {
+      // Cast to any to simulate a JavaScript consumer or handler with a missing return
+      const retryHandler = (async (_retryCtx: any) => {
+        // Intentionally no return statement — returns undefined
+      }) as any;
+      const result = yield ctx.callActivity(failingActivity, undefined, { retry: retryHandler });
+      return result;
+    };
+
+    taskHubWorker.addActivity(failingActivity);
+    taskHubWorker.addOrchestrator(orchestrator);
+    await taskHubWorker.start();
+
+    const id = await taskHubClient.scheduleNewOrchestration(orchestrator);
+    const state = await taskHubClient.waitForOrchestrationCompletion(id, undefined, 30);
+
+    expect(state).toBeDefined();
+    // Should fail after exactly 1 attempt — the handler returned undefined so no retry
+    expect(state?.runtimeStatus).toEqual(OrchestrationStatus.ORCHESTRATION_STATUS_FAILED);
+    expect(state?.failureDetails).toBeDefined();
+    expect(attemptCount).toBe(1);
+  }, 31000);
+
+  it("should fail (not retry infinitely) when retry handler returns null", async () => {
+    let attemptCount = 0;
+
+    const failingActivity = async (_: ActivityContext) => {
+      attemptCount++;
+      throw new Error(`Failure on attempt ${attemptCount}`);
+    };
+
+    const orchestrator: TOrchestrator = async function* (ctx: OrchestrationContext): any {
+      const retryHandler = async (_retryCtx: any) => {
+        return null as any; // Explicitly returning null
+      };
+      const result = yield ctx.callActivity(failingActivity, undefined, { retry: retryHandler });
+      return result;
+    };
+
+    taskHubWorker.addActivity(failingActivity);
+    taskHubWorker.addOrchestrator(orchestrator);
+    await taskHubWorker.start();
+
+    const id = await taskHubClient.scheduleNewOrchestration(orchestrator);
+    const state = await taskHubClient.waitForOrchestrationCompletion(id, undefined, 30);
+
+    expect(state).toBeDefined();
+    expect(state?.runtimeStatus).toEqual(OrchestrationStatus.ORCHESTRATION_STATUS_FAILED);
+    expect(state?.failureDetails).toBeDefined();
+    expect(attemptCount).toBe(1);
+  }, 31000);
+
+  it("should retry and succeed when retry handler returns true", async () => {
+    let attemptCount = 0;
+
+    const flakyActivity = async (_: ActivityContext, input: number) => {
+      attemptCount++;
+      if (attemptCount < 3) {
+        throw new Error(`Transient failure on attempt ${attemptCount}`);
+      }
+      return input * 2;
+    };
+
+    const orchestrator: TOrchestrator = async function* (ctx: OrchestrationContext, input: number): any {
+      const retryHandler = async (retryCtx: any) => retryCtx.lastAttemptNumber < 5;
+      const result = yield ctx.callActivity(flakyActivity, input, { retry: retryHandler });
+      return result;
+    };
+
+    taskHubWorker.addActivity(flakyActivity);
+    taskHubWorker.addOrchestrator(orchestrator);
+    await taskHubWorker.start();
+
+    const id = await taskHubClient.scheduleNewOrchestration(orchestrator, 21);
+    const state = await taskHubClient.waitForOrchestrationCompletion(id, undefined, 30);
+
+    expect(state).toBeDefined();
+    expect(state?.runtimeStatus).toEqual(OrchestrationStatus.ORCHESTRATION_STATUS_COMPLETED);
+    expect(state?.failureDetails).toBeUndefined();
+    expect(state?.serializedOutput).toEqual(JSON.stringify(42));
+    expect(attemptCount).toBe(3);
+  }, 31000);
+
+  it("should retry with delay when retry handler returns a positive number", async () => {
+    let attemptCount = 0;
+    const attemptTimes: number[] = [];
+
+    const flakyActivity = async (_: ActivityContext) => {
+      attemptCount++;
+      attemptTimes.push(Date.now());
+      if (attemptCount < 2) {
+        throw new Error(`Transient failure on attempt ${attemptCount}`);
+      }
+      return "success";
+    };
+
+    const orchestrator: TOrchestrator = async function* (ctx: OrchestrationContext): any {
+      const retryHandler = async (_retryCtx: any) => {
+        return 1000; // Retry after 1 second
+      };
+      const result = yield ctx.callActivity(flakyActivity, undefined, { retry: retryHandler });
+      return result;
+    };
+
+    taskHubWorker.addActivity(flakyActivity);
+    taskHubWorker.addOrchestrator(orchestrator);
+    await taskHubWorker.start();
+
+    const id = await taskHubClient.scheduleNewOrchestration(orchestrator);
+    const state = await taskHubClient.waitForOrchestrationCompletion(id, undefined, 30);
+
+    expect(state).toBeDefined();
+    expect(state?.runtimeStatus).toEqual(OrchestrationStatus.ORCHESTRATION_STATUS_COMPLETED);
+    expect(state?.failureDetails).toBeUndefined();
+    expect(state?.serializedOutput).toEqual(JSON.stringify("success"));
+    expect(attemptCount).toBe(2);
+
+    // Verify there was at least ~1s delay between attempts
+    if (attemptTimes.length >= 2) {
+      const delay = attemptTimes[1] - attemptTimes[0];
+      expect(delay).toBeGreaterThanOrEqual(900); // Allow some tolerance
+    }
+  }, 31000);
+
   // // ==================== newGuid Tests ====================
 
   it("should generate deterministic GUIDs with newGuid", async () => {