diff --git a/lib/low_balance.rb b/lib/low_balance.rb
index dbd445437a642666b6fbf267bd12df7fee5cec1c..bee120e524a335d884abc269d11c746d15ea0c6c 100644
--- a/lib/low_balance.rb
+++ b/lib/low_balance.rb
@@ -2,6 +2,7 @@
 
 require_relative "expiring_lock"
 require_relative "transaction"
+require_relative "credit_card_sale"
 
 class LowBalance
 	def self.for(customer, transaction_amount=0)