diff --git a/dist/types/classes/Currency.d.ts b/dist/types/classes/Currency.d.ts
index 1ffa298..914eec8 100644
--- a/dist/types/classes/Currency.d.ts
+++ b/dist/types/classes/Currency.d.ts
@@ -301,6 +301,6 @@ declare class CurrencyStatic<UpgradeInitArray extends Readonly<UpgradeInit>[] =
      * @param target - The target level or quantity to reach for the item. See the argument in {@link calculateItem}.
      * @returns Returns true if the purchase or upgrade is successful, or false if there is not enough currency or the item does not exist.
      */
-    buyItem(id: ItemIds, tier: DecimalSource, target?: DecimalSource): boolean;
+    buyItem(id: ItemIds, tier?: DecimalSource, target?: DecimalSource): boolean;
 }
 export { Currency, CurrencyStatic };
diff --git a/src/classes/Currency.ts b/src/classes/Currency.ts
index 045a4c4..e581f68 100644
--- a/src/classes/Currency.ts
+++ b/src/classes/Currency.ts
@@ -625,7 +625,7 @@ class CurrencyStatic<
      * @param target - The target level or quantity to reach for the item. See the argument in {@link calculateItem}.
      * @returns Returns true if the purchase or upgrade is successful, or false if there is not enough currency or the item does not exist.
      */
-    public buyItem (id: ItemIds, tier: DecimalSource, target?: DecimalSource): boolean {
+    public buyItem (id: ItemIds, tier?: DecimalSource, target?: DecimalSource): boolean {
         // Get the item
         const item = this.getItem(id);