diff --git a/unipay/providers/transfer.py b/unipay/providers/transfer.py
index d2de4ab..b409cb1 100644
--- a/unipay/providers/transfer.py
+++ b/unipay/providers/transfer.py
@@ -128,7 +128,7 @@ class TransferGateway(Gateway):
 	def gen_mailcode(self):
 		c = '1'
 		for i in range(6):
-			c += randint(0,9)
+			c += str(randint(0,9))
 		return c
 		
 	def run(self):