diff --git a/src/repositories/InMemoryNotificationRepository.ts b/src/repositories/InMemoryNotificationRepository.ts
index bd1db3f..513f7b7 100644
--- a/src/repositories/InMemoryNotificationRepository.ts
+++ b/src/repositories/InMemoryNotificationRepository.ts
@@ -107,6 +107,12 @@ export class InMemoryNotificationRepository implements NotificationRepository {
 
     const secondsThreshold = this.deviceIdsToDeliverTo[tupleKey.toString()][deviceId];
     delete this.deviceIdsToDeliverTo[tupleKey.toString()][deviceId];
+
+    if (Object.keys(this.deviceIdsToDeliverTo[tupleKey.toString()]).length === 0) {
+      // no more device IDs remaining for this key combination
+      delete this.deviceIdsToDeliverTo[tupleKey.toString()];
+    }
+
     this.listeners.forEach((listener) => {
       const event: NotificationEvent = {
         event: 'delete',