diff --git a/apps/pr-reviewer/fixtures/demo-pr/discount.ts b/apps/pr-reviewer/fixtures/demo-pr/discount.ts
index 6155246..ab7f51f 100644
--- a/apps/pr-reviewer/fixtures/demo-pr/discount.ts
+++ b/apps/pr-reviewer/fixtures/demo-pr/discount.ts
@@ -1,3 +1,4 @@
 export function applyDiscount(total: number, percent: number): number {
-  return total - total * percent;
+  const rate = Math.min(Math.max(percent, 0), 1);
+  return total - total * rate;
 }