diff --git a/tools/continuous_build/build_internal/scripts/clean_old_files.py b/tools/continuous_build/build_internal/scripts/clean_old_files.py
index 94e210aa7..3b26bb513 100755
--- a/tools/continuous_build/build_internal/scripts/clean_old_files.py
+++ b/tools/continuous_build/build_internal/scripts/clean_old_files.py
@@ -7,7 +7,7 @@
 #  in the file PATENTS.  All contributing project authors may
 #  be found in the AUTHORS file in the root of the source tree.
 
-__author__ = "ivinnichenko@webrtc.org (Illya Vinnichenko)"
+__author__ = 'ivinnichenko@webrtc.org (Illya Vinnichenko)'
 
 """This script will prune sufficiently old files and empty directories.
 
@@ -26,16 +26,16 @@ import time
 
 # The path is considered whitelisted if any of these entries appear
 # at some point in the path
-WHITELIST = ["buildbot.tac", "master.cfg", "public_html", "changes.pck",
-             "webrtc_buildbot"]
+WHITELIST = ['buildbot', 'buildbot.tac', 'Makefile', 'master.cfg',
+             'public_html', 'slaves.cfg', 'state.sqlite', 'twistd.pid']
 
 
 def is_whitelisted(path):
-  """Check if file is whitelisted.
+  '''Check if file is whitelisted.
 
     Args:
       path: file path.
-  """
+  '''
   for entry in WHITELIST:
     if entry in path:
       return True
@@ -47,11 +47,11 @@ def delete_directory(directory):
     os.rmdir(directory)
     return True
   except OSError as exception:
-    if "not empty" in str(exception):
+    if 'not empty' in str(exception):
       # This is normal, ignore it
       pass
     else:
-      print "Could not remove directory %s: reason %s." % (directory, exception)
+      print 'Could not remove directory %s: reason %s.' % (directory, exception)
   return False
 
 
@@ -59,19 +59,19 @@ def delete_file(file):
   try:
     os.remove(file)
   except OSError as exception:
-    print "Unexpectedly failed to remove file %s: reason %s." % (file,
+    print 'Unexpectedly failed to remove file %s: reason %s.' % (file,
                                                                  exception)
 
 
 def log_removal(file_or_directory, time_stamp, verbose):
   if verbose:
-    str_stamp = time.strftime("%a, %d %b %Y %H:%M:%S +0000",
+    str_stamp = time.strftime('%a, %d %b %Y %H:%M:%S +0000',
                               time.gmtime(time_stamp))
-    print "Removing [%s], stamped on %s" % (file_or_directory, str_stamp)
+    print 'Removing [%s], stamped on %s' % (file_or_directory, str_stamp)
 
 
 def remove_old_files_and_directories(path, num_days, verbose, skip_dirs):
-  """Removes all files under path that are older than num_days days.
+  '''Removes all files under path that are older than num_days days.
      The algorithm also tried to delete all directories, except for those who
      contain files that are sufficiently new.
 
@@ -82,7 +82,7 @@ def remove_old_files_and_directories(path, num_days, verbose, skip_dirs):
       path: The starting point.
       num_days: days limit for removal.
       verbose: print every cmd?
-  """
+  '''
   current_time = time.time()
   limit = 60 * 60 * 24 * num_days
 
@@ -108,30 +108,30 @@ def remove_old_files_and_directories(path, num_days, verbose, skip_dirs):
 
 
 def main():
-  usage = "usage: %prog -p <base path> -n <number of days> [-q] [-d]"
+  usage = 'usage: %prog -p <base path> -n <number of days> [-q] [-d]'
   parser = OptionParser(usage)
-  parser.add_option("-p", "--path", dest="cleanup_path", help="base directory")
-  parser.add_option("-n", "--num_days", dest="num_days", help="number of days")
-  parser.add_option("-q", "--quiet",
-                    action="store_false", dest="verbose", default=True,
-                    help="don't print status messages to stdout")
-  parser.add_option("-d", "--delete-dirs-too",
-                    action="store_false", dest="skip_dirs", default=True,
-                    help="number of days")
+  parser.add_option('-p', '--path', dest='cleanup_path', help='base directory')
+  parser.add_option('-n', '--num_days', dest='num_days', help='number of days')
+  parser.add_option('-q', '--quiet',
+                    action='store_false', dest='verbose', default=True,
+                    help='do not print status messages to stdout')
+  parser.add_option('-d', '--delete-dirs-too',
+                    action='store_false', dest='skip_dirs', default=True,
+                    help='number of days')
 
   options, args = parser.parse_args()
   if not options.cleanup_path:
-    print "You must specify base directory"
+    print 'You must specify base directory'
     sys.exit(2)
   if not options.num_days:
-    print "You must specify number of days old"
+    print 'You must specify number of days old'
     sys.exit(2)
 
   if options.verbose:
-    print "Cleaning up everything in %s older than %s days" % (
+    print 'Cleaning up everything in %s older than %s days' % (
         options.cleanup_path, options.num_days)
   remove_old_files_and_directories(options.cleanup_path, int(options.num_days),
                                    options.verbose, options.skip_dirs)
 
-if __name__ == "__main__":
+if __name__ == '__main__':
   main()