diff --git a/eopayment/dummy.py b/eopayment/dummy.py
index 62eb9f9..97b879f 100644
--- a/eopayment/dummy.py
+++ b/eopayment/dummy.py
@@ -12,7 +12,7 @@ from .common import PaymentCommon, URL, PaymentResponse, PAID, ERROR, WAITING, R
 __all__ = [ 'Payment' ]
 
 SERVICE_URL = 'http://dummy-payment.demo.entrouvert.com/'
-ALPHANUM = string.letters + string.digits
+ALPHANUM = string.ascii_letters + string.digits
 LOGGER = logging.getLogger(__name__)
 
 class Payment(PaymentCommon):
diff --git a/eopayment/spplus.py b/eopayment/spplus.py
index 3bbcd50..ab27f29 100644
--- a/eopayment/spplus.py
+++ b/eopayment/spplus.py
@@ -89,7 +89,7 @@ def sign_url_paiement(ntkey, query):
     data_to_sign = ''.join(fields)
     return hmac.new(key[:20], data_to_sign, hashlib.sha1).hexdigest().upper()
 
-ALPHANUM = string.letters + string.digits
+ALPHANUM = string.ascii_letters + string.digits
 SERVICE_URL = "https://www.spplus.net/paiement/init.do"
 
 class Payment(PaymentCommon):