diff --git a/lib/pay_zen/helper.rb b/lib/pay_zen/helper.rb
index 047980920..ea98c972b 100644
--- a/lib/pay_zen/helper.rb
+++ b/lib/pay_zen/helper.rb
@@ -19,10 +19,10 @@ class PayZen::Helper
     end
 
     ## generate an unique string reference for the content of a cart
-    def generate_ref(cart_items, customer, date = DateTime.current)
+    def generate_ref(cart_items, customer)
       require 'sha3'
 
-      content = { cart_items: cart_items, customer: customer }.to_json + date.to_s
+      content = { cart_items: cart_items, customer: customer }.to_json + DateTime.current.to_s
       # It's safe to truncate a hash. See https://crypto.stackexchange.com/questions/74646/sha3-255-one-bit-less
       SHA3::Digest.hexdigest(:sha224, content)[0...24]
     end
diff --git a/test/integration/payzen_test.rb b/test/integration/payzen_test.rb
index 83c1ac81d..42b529b1c 100644
--- a/test/integration/payzen_test.rb
+++ b/test/integration/payzen_test.rb
@@ -93,7 +93,7 @@ class PayzenTest < ActionDispatch::IntegrationTest
     cs = CartService.new(@user)
     cart = cs.from_hash(cart_items)
     amount = cart.total[:total]
-    id = PayZen::Helper.generate_ref(cart_items, @user.id, DateTime.new(1970, 1, 1, 0, 0, 0))
+    id = 'dffd53627a4901e986862674'
 
     VCR.use_cassette('confirm_payzen_payment_success') do
       client = PayZen::PCI::Charge.new