diff --git a/lib/TierCortex.ts b/lib/TierCortex.ts
index d1cdb8a..cc67a79 100644
--- a/lib/TierCortex.ts
+++ b/lib/TierCortex.ts
@@ -150,18 +150,18 @@ export class TierCortex {
       if (decodedState) return decodedState.tiers;
     }
 
+    const initialTiers: Tier[] = JSON.parse(JSON.stringify(DEFAULT_TIER_TEMPLATE));
+
     if (initialItemSet) {
-      const initialTiers = [...DEFAULT_TIER_TEMPLATE];
       const lastTierIndex = initialTiers.length - 1;
 
       initialTiers[lastTierIndex].items = initialItemSet.images.map((filename) => {
         const itemId = `${initialItemSet.packageName}-${filename}`;
         return this.packageItemLookup[itemId] || this.createPlaceholderItem(itemId, filename);
       });
-      return initialTiers;
     }
 
-    return DEFAULT_TIER_TEMPLATE;
+    return initialTiers;
   }
 
   public getOgSafeImageUrl(url: string): string {
diff --git a/models/Tier.ts b/models/Tier.ts
index 3500e84..98650dd 100644
--- a/models/Tier.ts
+++ b/models/Tier.ts
@@ -10,7 +10,7 @@ export default interface Tier {
   placeholder?: string;
 }
 
-export type TierTemplate = Record<string, Tier[]>;
+export type TierTemplate = Record<string, Readonly<Tier>[]>;
 
 export const tierTemplates: TierTemplate = {
   '3rows': [