diff --git a/lib/stripe/resources/bank_account.rb b/lib/stripe/resources/bank_account.rb
index 3b578f13b..180b1d218 100644
--- a/lib/stripe/resources/bank_account.rb
+++ b/lib/stripe/resources/bank_account.rb
@@ -94,10 +94,12 @@ def self.verify(customer, id, params = {}, opts = {})
     end
 
     def resource_url
-      if respond_to?(:customer)
+      if !customer.nil?
         "#{Customer.resource_url}/#{CGI.escape(customer)}/sources/#{CGI.escape(id)}"
-      elsif respond_to?(:account)
+      elsif !account.nil?
         "#{Account.resource_url}/#{CGI.escape(account)}/external_accounts/#{CGI.escape(id)}"
+      else
+        raise InvalidRequestError, "Could not determine which URL to request: [account, customer] fields are all null"
       end
     end