diff --git a/addons/base_iban/base_iban.py b/addons/base_iban/base_iban.py
index 92783b8eb74..d1bc2daf61d 100644
--- a/addons/base_iban/base_iban.py
+++ b/addons/base_iban/base_iban.py
@@ -67,7 +67,7 @@ def _format_iban(string):
     res = ""
     for char in string:
         if char.isalnum():
-            res += char.lower()
+            res += char.upper()
     return res
 
 class res_partner_bank(osv.osv):
@@ -92,7 +92,7 @@ class res_partner_bank(osv.osv):
         for bank_acc in self.browse(cr, uid, ids):
             if not bank_acc.iban:
                 continue
-            iban = _format_iban(bank_acc.iban)
+            iban = _format_iban(bank_acc.iban).lower()
             if iban[:2] in _iban_len and len(iban) != _iban_len[iban[:2]]:
                 return False
             #the four first digits have to be shifted to the end