1 files changed, 2 insertions, 6 deletions

diff --git a/src/mailman/chains/headers.py b/src/mailman/chains/headers.py
index 7628c8b7c..5738336e8 100644
--- a/src/mailman/chains/headers.py
+++ b/src/mailman/chains/headers.py
@@ -17,9 +17,6 @@
 
 """The header-matching chain."""
 
-from __future__ import absolute_import, print_function, unicode_literals
-
-__metaclass__ = type
 __all__ = [
     'HeaderMatchChain',
     ]
@@ -28,13 +25,12 @@ __all__ = [
 import re
 import logging
 
-from zope.interface import implementer
-
 from mailman.chains.base import Chain, Link
 from mailman.config import config
 from mailman.core.i18n import _
 from mailman.interfaces.chain import LinkAction
 from mailman.interfaces.rules import IRule
+from zope.interface import implementer
 
 
 log = logging.getLogger('mailman.error')
@@ -122,7 +118,7 @@ class HeaderMatchChain(Chain):
         """See `IMutableChain`."""
         # Remove all dynamically created rules.  Use the keys so we can mutate
         # the dictionary inside the loop.
-        for rule_name in config.rules.keys():
+        for rule_name in list(config.rules):
             if rule_name.startswith('header-match-'):
                 del config.rules[rule_name]
         self._extended_links = []