diff --git a/apps/webapp/app/v3/services/createBackgroundWorker.server.test.ts b/apps/webapp/app/v3/services/createBackgroundWorker.server.test.ts
index 147721ecfef..ae58319fd2c 100644
--- a/apps/webapp/app/v3/services/createBackgroundWorker.server.test.ts
+++ b/apps/webapp/app/v3/services/createBackgroundWorker.server.test.ts
@@ -121,7 +121,7 @@ const asEnv = (
     organization: { id: env.organizationId, featureFlags: organizationFeatureFlags },
   }) as unknown as AuthenticatedEnvironment;
 
-function declarativeTasks(schedule: { cron: string; timezone: string; window?: string }): TasksArg {
+function declarativeTasks(schedule: { cron: string; timezone?: string; window?: string }): TasksArg {
   return [{ id: "my-task", schedule }] as TasksArg;
 }
 
@@ -488,6 +488,42 @@ describe("syncDeclarativeSchedules registration", () => {
     }
   );
 
+  containerTest(
+    "preserves an existing Redis job when task schedule omits explicit timezone (defaults to UTC)",
+    async ({ prisma, redisOptions }) => {
+      const { project, prodEnv } = await seedProjectWithEnvs(prisma);
+      const schedule = await makeDeclarativeSchedule(prisma, project.id, [prodEnv.id]);
+      const updatedAt = schedule.updatedAt;
+      await seedScheduledTask(prisma, project.id, prodEnv.id);
+      const engine = createTestScheduleEngine(prisma, redisOptions);
+
+      try {
+        const jobId = scheduleJobId(schedule.instances[0].id);
+        await engine.registerNextTaskScheduleInstance({ instanceId: schedule.instances[0].id });
+        const before = await engine.getJob(jobId);
+
+        await syncDeclarativeSchedules(
+          declarativeTasks({ cron: "0 * * * *" }),
+          noWorker,
+          asEnv(prodEnv),
+          prisma,
+          engine
+        );
+
+        expect(before).toBeDefined();
+        expect(await engine.getJob(jobId)).toEqual(before);
+        expect(
+          await prisma.taskSchedule.findUniqueOrThrow({
+            where: { id: schedule.id },
+            select: { updatedAt: true },
+          })
+        ).toEqual({ updatedAt });
+      } finally {
+        await engine.quit();
+      }
+    }
+  );
+
   containerTest(
     "replaces the Redis job when declarative timing changes",
     async ({ prisma, redisOptions }) => {
diff --git a/apps/webapp/app/v3/services/createBackgroundWorker.server.ts b/apps/webapp/app/v3/services/createBackgroundWorker.server.ts
index bbdfee76e85..e76e6bd7d39 100644
--- a/apps/webapp/app/v3/services/createBackgroundWorker.server.ts
+++ b/apps/webapp/app/v3/services/createBackgroundWorker.server.ts
@@ -1528,7 +1528,7 @@ async function prepareDeclarativeSchedules(
       }
       assertCronMeetsFreeMinimum({
         cron: task.schedule.cron,
-        timezone: task.schedule.timezone,
+        timezone: task.schedule.timezone ?? "UTC",
         minimumWindowDurationSeconds,
         scheduleType: "DECLARATIVE",
         environmentType: environment.type,
@@ -1540,7 +1540,7 @@ async function prepareDeclarativeSchedules(
         taskId: task.id,
         explicitWindow: task.schedule.window,
         cron: task.schedule.cron,
-        timezone: task.schedule.timezone,
+        timezone: task.schedule.timezone ?? "UTC",
         defaultWindowDurationSeconds,
         minimumWindowDurationSeconds,
       });
@@ -1588,7 +1588,7 @@ export async function syncDeclarativeSchedules(
         environment.projectId,
         {
           cron: task.schedule.cron,
-          timezone: task.schedule.timezone,
+          timezone: task.schedule.timezone ?? "UTC",
           taskIdentifier: task.id,
           friendlyId: existingSchedule?.friendlyId,
           window: task.schedule.window,
@@ -1610,6 +1610,7 @@ export async function syncDeclarativeSchedules(
   const apply = async (db: PrismaClientOrTransaction) => {
     for (const { task, existingSchedule, minimumWindowDurationSeconds } of preparedTasks) {
       const normalizedWindow = normalizeScheduleWindow(task.schedule.window);
+      const nextTimezone = task.schedule.timezone ?? "UTC";
 
       if (existingSchedule) {
         // Compare effective windows so equivalent explicit/default values preserve the pending job.
@@ -1625,13 +1626,13 @@ export async function syncDeclarativeSchedules(
         }).window;
         const timingChanged =
           existingSchedule.generatorExpression !== task.schedule.cron ||
-          existingSchedule.timezone !== task.schedule.timezone ||
+          existingSchedule.timezone !== nextTimezone ||
           !scheduleWindowsEqual(previousWindow, nextWindow) ||
           // Clearing the minimum changes the effective range.
           existingSchedule.minimumWindowDurationSeconds !== minimumWindowDurationSeconds;
         const persistedValuesChanged =
           existingSchedule.generatorExpression !== task.schedule.cron ||
-          existingSchedule.timezone !== task.schedule.timezone ||
+          existingSchedule.timezone !== nextTimezone ||
           existingSchedule.windowDurationSeconds !== normalizedWindow.windowDurationSeconds ||
           existingSchedule.windowPercentage !== normalizedWindow.windowPercentage ||
           existingSchedule.minimumWindowDurationSeconds !== minimumWindowDurationSeconds;
@@ -1643,7 +1644,7 @@ export async function syncDeclarativeSchedules(
               data: {
                 generatorExpression: task.schedule.cron,
                 generatorDescription: cronstrue.toString(task.schedule.cron),
-                timezone: task.schedule.timezone,
+                timezone: nextTimezone,
                 minimumWindowDurationSeconds,
                 ...normalizedWindow,
               },
@@ -1675,7 +1676,7 @@ export async function syncDeclarativeSchedules(
             taskIdentifier: task.id,
             generatorExpression: task.schedule.cron,
             generatorDescription: cronstrue.toString(task.schedule.cron),
-            timezone: task.schedule.timezone,
+            timezone: nextTimezone,
             type: "DECLARATIVE",
             minimumWindowDurationSeconds,
             ...normalizedWindow,