diff --git a/contrib/linearize/linearize-hashes.py b/contrib/linearize/linearize-hashes.py
index 348ea6aa7e..555ff2926b 100755
--- a/contrib/linearize/linearize-hashes.py
+++ b/contrib/linearize/linearize-hashes.py
@@ -1,143 +1,143 @@
 #!/usr/bin/env python3
 #
 # linearize-hashes.py:  List blocks in a linear, no-fork version of the chain.
 #
 # Copyright (c) 2013-2016 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 #
 
 from __future__ import print_function
 try:  # Python 3
     import http.client as httplib
 except ImportError:  # Python 2
     import httplib
 import json
 import re
 import base64
 import sys
 
 settings = {}
 
 ##### Switch endian-ness #####
 
 
 def hex_switchEndian(s):
     """ Switches the endianness of a hex string (in pairs of hex chars) """
     pairList = [s[i:i + 2].encode() for i in range(0, len(s), 2)]
     return b''.join(pairList[::-1]).decode()
 
 
 class BitcoinRPC:
     def __init__(self, host, port, username, password):
         authpair = "%s:%s" % (username, password)
         authpair = authpair.encode('utf-8')
         self.authhdr = b"Basic " + base64.b64encode(authpair)
         self.conn = httplib.HTTPConnection(host, port=port, timeout=30)
 
     def execute(self, obj):
         try:
             self.conn.request('POST', '/', json.dumps(obj),
                               {'Authorization': self.authhdr,
                                'Content-type': 'application/json'})
         except ConnectionRefusedError:
             print('RPC connection refused. Check RPC settings and the server status.',
                   file=sys.stderr)
             return None
 
         resp = self.conn.getresponse()
         if resp is None:
             print("JSON-RPC: no response", file=sys.stderr)
             return None
 
         body = resp.read().decode('utf-8')
         resp_obj = json.loads(body)
         return resp_obj
 
     @staticmethod
     def build_request(idx, method, params):
         obj = {'version': '1.1',
                'method': method,
                'id': idx}
         if params is None:
             obj['params'] = []
         else:
             obj['params'] = params
         return obj
 
     @staticmethod
     def response_is_error(resp_obj):
         return 'error' in resp_obj and resp_obj['error'] is not None
 
 
 def get_block_hashes(settings, max_blocks_per_call=10000):
     rpc = BitcoinRPC(settings['host'], settings['port'],
                      settings['rpcuser'], settings['rpcpassword'])
 
     height = settings['min_height']
     while height < settings['max_height'] + 1:
         num_blocks = min(settings['max_height'] +
                          1 - height, max_blocks_per_call)
         batch = []
         for x in range(num_blocks):
             batch.append(rpc.build_request(x, 'getblockhash', [height + x]))
 
         reply = rpc.execute(batch)
         if reply is None:
             print('Cannot continue. Program will halt.')
             return None
 
         for x, resp_obj in enumerate(reply):
             if rpc.response_is_error(resp_obj):
                 print('JSON-RPC: error at height', height + x,
                       ': ', resp_obj['error'], file=sys.stderr)
                 exit(1)
             assert(resp_obj['id'] == x)  # assume replies are in-sequence
             if settings['rev_hash_bytes'] == 'true':
                 resp_obj['result'] = hex_switchEndian(resp_obj['result'])
             print(resp_obj['result'])
 
         height += num_blocks
 
 
 if __name__ == '__main__':
     if len(sys.argv) != 2:
         print("Usage: linearize-hashes.py CONFIG-FILE")
         sys.exit(1)
 
     f = open(sys.argv[1])
     for line in f:
         # skip comment lines
         m = re.search('^\s*#', line)
         if m:
             continue
 
         # parse key=value lines
         m = re.search('^(\w+)\s*=\s*(\S.*)$', line)
         if m is None:
             continue
         settings[m.group(1)] = m.group(2)
     f.close()
 
     if 'host' not in settings:
         settings['host'] = '127.0.0.1'
     if 'port' not in settings:
         settings['port'] = 8332
     if 'min_height' not in settings:
         settings['min_height'] = 0
     if 'max_height' not in settings:
         settings['max_height'] = 313000
     if 'rev_hash_bytes' not in settings:
         settings['rev_hash_bytes'] = 'false'
     if 'rpcuser' not in settings or 'rpcpassword' not in settings:
-        print("Missing username and/or password in cfg file", file=stderr)
+        print("Missing username and/or password in cfg file", file=sys.stderr)
         sys.exit(1)
 
     settings['port'] = int(settings['port'])
     settings['min_height'] = int(settings['min_height'])
     settings['max_height'] = int(settings['max_height'])
 
     # Force hash byte format setting to be lowercase to make comparisons easier.
     settings['rev_hash_bytes'] = settings['rev_hash_bytes'].lower()
 
     get_block_hashes(settings)