diff --git a/app/models/spree/payment_method_decorator.rb b/app/models/spree/payment_method_decorator.rb
index 32819544ed..3b9eff2cab 100644
--- a/app/models/spree/payment_method_decorator.rb
+++ b/app/models/spree/payment_method_decorator.rb
@@ -40,7 +40,7 @@ Spree::PaymentMethod.class_eval do
 
   def init
     unless reflections.keys.include? :calculator
-      include Spree::Core::CalculatedAdjustments
+      self.class.include Spree::Core::CalculatedAdjustments
     end
 
     self.calculator ||= Spree::Calculator::FlatRate.new(preferred_amount: 0)