diff --git a/src/loadgenerator/locustfile.py b/src/loadgenerator/locustfile.py
index eb81322..2167799 100644
--- a/src/loadgenerator/locustfile.py
+++ b/src/loadgenerator/locustfile.py
@@ -59,6 +59,10 @@ def addToCart(l):
 
 def checkout(l):
     addToCart(l)
+    # For five minutes every other hour, credit cards passed by the user will be
+    # invalid and the paymentservice will fail.
+    now = time.localtime()
+    expiration_year = '2015' if (now.tm_hour % 2) & (now.tm_min < 5) else '2060'
     l.client.post("/cart/checkout", {
         'email': 'someone@example.com',
         'street_address': '1600 Amphitheatre Parkway',
@@ -68,7 +72,7 @@ def checkout(l):
         'country': 'United States',
         'credit_card_number': '4432-8015-6152-0454',
         'credit_card_expiration_month': '1',
-        'credit_card_expiration_year': '2039',
+        'credit_card_expiration_year': expiration_year,
         'credit_card_cvv': '672',
     })
 
diff --git a/src/paymentservice/charge.js b/src/paymentservice/charge.js
index ce9674a..fe7b9da 100644
--- a/src/paymentservice/charge.js
+++ b/src/paymentservice/charge.js
@@ -15,6 +15,7 @@
 const cardValidator = require('simple-card-validator');
 const uuid = require('uuid/v4');
 const pino = require('pino');
+const grpc = require('grpc');
 
 const logger = pino({
   name: 'paymentservice-charge',
@@ -28,6 +29,7 @@ class CreditCardError extends Error {
   constructor (message) {
     super(message);
     this.code = 400; // Invalid argument error
+    this.status = grpc.status.INVALID_ARGUMENT;
   }
 }