diff --git a/src/index.spec.ts b/src/index.spec.ts
index c30a469..acf1138 100644
--- a/src/index.spec.ts
+++ b/src/index.spec.ts
@@ -7,15 +7,15 @@ describe('Multi currency money', () => {
     it('should multiply $5 by 2 and get $10', () => {
       const five = new Dollar(5);
       const product = five.times(2);
-      expect(product.amount).toEqual(10);
+      expect(product.equals(new Dollar(10))).toBe(true);
     });
 
     it('should preserve the initial dollar amount when multiplying multiple times', () => {
       const five = new Dollar(5);
       let product: Dollar = five.times(2);
-      expect(product.amount).toEqual(10);
+      expect(product.equals(new Dollar(10))).toBe(true);
       product = five.times(3);
-      expect(product.amount).toEqual(15);
+      expect(product.equals(new Dollar(15))).toBe(true);
     });
   });
 
diff --git a/src/index.ts b/src/index.ts
index 9045ade..53c2083 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,5 @@
 export default class Dollar {
-  amount: number;
+  private amount: number;
 
   constructor(amount: number) {
     this.amount = amount;