diff --git a/card_num_generator.py b/card_num_generator.py
index 7260350..29bc2f6 100644
--- a/card_num_generator.py
+++ b/card_num_generator.py
@@ -65,7 +65,9 @@ def finalize(nums):
                 check_sum += n_ -9 if n_ > 9 else n_
             else:
                 check_sum += n
-        return nums + [10 - (check_sum % 10) ]
+        n1 = 10 - (check_sum % 10)
+        if n1>9: n1=0
+        return nums + [ n1 ]
     
     # main body
     t = type.lower()