diff --git a/app/config/contributions.js b/app/config/contributions.js
index 7d8cab2..73005f1 100644
--- a/app/config/contributions.js
+++ b/app/config/contributions.js
@@ -8,7 +8,7 @@ export const CONTRIBUTION_PRESETS = [
   { amount: 50, label: "I want to sponsor multiple members" },
 ]
 
-export const requiresPayment = (amount) => Number(amount) > 0
+export const requiresPayment = (amount) => amount > 0
 
 export const isValidContributionAmount = (amount) =>
   Number.isInteger(amount) && amount >= 0
@@ -17,6 +17,6 @@ export const getGuidanceLabel = (amount) => {
   if (amount === null || amount === undefined) return null
   const n = Number(amount)
   if (!Number.isFinite(n) || n < 0) return null
-  const match = [...CONTRIBUTION_PRESETS].reverse().find(p => p.amount <= n)
+  const match = CONTRIBUTION_PRESETS.findLast(p => p.amount <= n)
   return match?.label ?? null
 }
diff --git a/tests/client/contributions.test.js b/tests/client/contributions.test.js
index fff5db4..7bda7a3 100644
--- a/tests/client/contributions.test.js
+++ b/tests/client/contributions.test.js
@@ -26,9 +26,10 @@ describe('requiresPayment', () => {
     expect(requiresPayment(1)).toBe(true)
     expect(requiresPayment(15)).toBe(true)
   })
-  it('coerces string numbers', () => {
-    expect(requiresPayment('15')).toBe(true)
-    expect(requiresPayment('0')).toBe(false)
+  it('returns false for null, undefined, NaN', () => {
+    expect(requiresPayment(null)).toBe(false)
+    expect(requiresPayment(undefined)).toBe(false)
+    expect(requiresPayment(NaN)).toBe(false)
   })
 })