diff --git a/src/actors/runtime/AbstractActor.ts b/src/actors/runtime/AbstractActor.ts
index 37329e0e..60bb84b2 100644
--- a/src/actors/runtime/AbstractActor.ts
+++ b/src/actors/runtime/AbstractActor.ts
@@ -96,7 +96,7 @@ export default abstract class AbstractActor {
     reminderName: string,
     dueTime: Temporal.Duration,
     period: Temporal.Duration | undefined,
-    ttl?: Temporal.Duration,
+    ttl?: Temporal.Duration | undefined,
     state?: any,
   ) {
     await this.actorClient.actor.registerActorReminder(this.actorType, this.id, reminderName, {
diff --git a/src/types/ActorReminder.type.ts b/src/types/ActorReminder.type.ts
index 06912b03..9d48308b 100644
--- a/src/types/ActorReminder.type.ts
+++ b/src/types/ActorReminder.type.ts
@@ -17,5 +17,5 @@ export type ActorReminderType = {
   period: Temporal.Duration | undefined; // e.g. 0h0m9s0ms
   dueTime?: Temporal.Duration; // e.g. 1m or 0h0m0s0ms defaults to 0s
   data?: any; // the data to pass
-  ttl?: Temporal.Duration; // e.g. 1m
+  ttl?: Temporal.Duration | undefined; // e.g. 1m
 };