diff --git a/src/app/checkout/client.tsx b/src/app/checkout/client.tsx
index 22d3366..3199a2e 100644
--- a/src/app/checkout/client.tsx
+++ b/src/app/checkout/client.tsx
@@ -55,6 +55,9 @@ export default function CheckoutPageClient({ isLoggedIn, customer }: CheckoutPag
     setCheckingOut(true);
     setCheckoutError(null);
     try {
+      // Mark that we're checking out so LogoutOnUnload doesn't clear cart
+      sessionStorage.setItem('isCheckingOut', 'true');
+
       const res = await fetch('/api/checkout', {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
@@ -70,6 +73,7 @@ export default function CheckoutPageClient({ isLoggedIn, customer }: CheckoutPag
       });
       const data = await res.json();
       if (!res.ok || !data.url) {
+        sessionStorage.removeItem('isCheckingOut');
         throw new Error(data.error ?? 'Something went wrong starting checkout.');
       }
       window.location.href = data.url;