Index: src/z3c/schema/payments/field.py
===================================================================
--- src/z3c/schema/payments/field.py	(revision 122267)
+++ src/z3c/schema/payments/field.py	(working copy)
@@ -27,7 +27,7 @@
        is low and pre-validating is fast"""
     
     financialIndustries = ['3','4','5','6']
-    if cardNum[1] not in financialIndustries:
+    if cardNum[0] not in financialIndustries:
         return False
         
     total = pos = 0
