diff --git a/src/business.js b/src/business.js
index a8f0cd0..8a8a7bb 100644
--- a/src/business.js
+++ b/src/business.js
@@ -12,8 +12,7 @@ function calculateDiscountedPrice(price, discountPercent) {
 }
 
 function totalCart(items) {
-  // BUG: ignores quantity, so multi-quantity line items are undercounted.
-  return roundToCents(items.reduce((total, item) => total + item.price, 0));
+  return roundToCents(items.reduce((total, item) => total + item.price * item.quantity, 0));
 }
 
 function normalizeUsername(username) {
diff --git a/test/business.test.js b/test/business.test.js
index e84f4fa..5823775 100644
--- a/test/business.test.js
+++ b/test/business.test.js
@@ -22,7 +22,10 @@ test('cart total includes item quantities', () => {
     { name: 'Notebook', price: 2.5, quantity: 2 },
   ];
 
-  assert.equal(totalCart(items), 17);
+  const total = totalCart(items);
+
+  assert.notEqual(total, 5.5);
+  assert.equal(total, 17);
 });
 
 test('username normalization trims, lowercases, and collapses whitespace', () => {