diff --git a/trustify/client/payment_challenge.py b/trustify/client/payment_challenge.py
index 9bef7594d..fc6171a68 100644
--- a/trustify/client/payment_challenge.py
+++ b/trustify/client/payment_challenge.py
@@ -20,9 +20,9 @@ class Payment_Challenge(Challenge):
         
     def perform(self, quiet=True):
         if quiet:
-            dialog.Dialog().msgbox(get_display_string(), width=70)
+            dialog.Dialog().msgbox(self.get_display_string(), width=70)
         else:
-            print get_display_string()
+            print self.get_display_string()
             raw_input('')
 
         self.times_performed += 1