diff --git a/src/notifications/schedulers/ETANotificationScheduler.ts b/src/notifications/schedulers/ETANotificationScheduler.ts
index 76c6027..4e0227a 100644
--- a/src/notifications/schedulers/ETANotificationScheduler.ts
+++ b/src/notifications/schedulers/ETANotificationScheduler.ts
@@ -75,12 +75,13 @@ export class ETANotificationScheduler {
 
   private async etaSubscriberCallback(eta: IEta) {
     const tuple = new TupleKey(eta.shuttleId, eta.stopId);
-    if (this.deviceIdsToDeliverTo[tuple.toString()] === undefined) {
+    const tupleKey = tuple.toString();
+    if (this.deviceIdsToDeliverTo[tupleKey] === undefined) {
       return;
     }
 
     const deviceIdsToRemove = new Set<string>();
-    for (let deviceId of Object.keys(this.deviceIdsToDeliverTo[tuple.toString()])) {
+    for (let deviceId of Object.keys(this.deviceIdsToDeliverTo[tupleKey])) {
       const deliveredSuccessfully = await this.sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold(deviceId, eta);
       if (deliveredSuccessfully) {
         deviceIdsToRemove.add(deviceId);
@@ -88,7 +89,7 @@ export class ETANotificationScheduler {
     }
 
     deviceIdsToRemove.forEach((deviceId) => {
-      delete this.deviceIdsToDeliverTo[tuple.toString()][deviceId]
+      delete this.deviceIdsToDeliverTo[tupleKey][deviceId]
     });
   }