diff --git a/lib/stripe/application_fee.rb b/lib/stripe/application_fee.rb
index 493914fe..16c47610 100644
--- a/lib/stripe/application_fee.rb
+++ b/lib/stripe/application_fee.rb
@@ -8,7 +8,7 @@ module Stripe
 
     def refund(params={}, opts={})
       api_key, headers = Util.parse_opts(opts)
-      response, api_key = Stripe.request(:post, refund_url, api_key, params, headers)
+      response, api_key = Stripe.request(:post, refund_url, api_key || @api_key, params, headers)
       refresh_from(response, api_key)
     end