diff --git a/.travis.yml b/.travis.yml
index 4a88b7764..4fbe78c2c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,7 +9,7 @@ cache:
     - dante-1.4.0
 before_install:
   - sudo apt-get update -qq
-  - sudo apt-get install -qq build-essential libssl-dev swig python-m2crypto python-numpy dnsutils iproute nginx
+  - sudo apt-get install -qq build-essential libssl-dev swig python-m2crypto python-numpy dnsutils iproute nginx bc
   - sudo dd if=/dev/urandom of=/usr/share/nginx/www/file bs=1M count=10
   - sudo service nginx restart
   - pip install m2crypto salsa20 pep8 pyflakes nose coverage
diff --git a/shadowsocks/utils.py b/shadowsocks/utils.py
index 7caa2434e..ff6801cd8 100644
--- a/shadowsocks/utils.py
+++ b/shadowsocks/utils.py
@@ -29,7 +29,7 @@
 import sys
 import getopt
 import logging
-from shadowsocks.common import to_bytes
+from shadowsocks.common import to_bytes, to_str
 
 
 VERBOSE_LEVEL = 5
@@ -73,7 +73,7 @@ def check_config(config):
         logging.warn('warning: local set to listen on 0.0.0.0, it\'s not safe')
     if config.get('server', '') in [b'127.0.0.1', b'localhost']:
         logging.warn('warning: server set to listen on %s:%s, are you sure?' %
-                     (config['server'], config['server_port']))
+                     (to_str(config['server']), config['server_port']))
     if (config.get('method', '') or '').lower() == b'table':
         logging.warn('warning: table is not safe; please use a safer cipher, '
                      'like AES-256-CFB')