diff --git a/brozzler/chrome.py b/brozzler/chrome.py
index e9d3ef0..f72ff8d 100644
--- a/brozzler/chrome.py
+++ b/brozzler/chrome.py
@@ -117,7 +117,7 @@ class Chrome:
         # these can raise exceptions
         self._home_tmpdir = tempfile.TemporaryDirectory()
         self._chrome_user_data_dir = os.path.join(
-            self._home_tmpdir.name, 'chrome-user-data'),
+            self._home_tmpdir.name, 'chrome-user-data')
         self._init_cookie_db()
 
         new_env = os.environ.copy()
@@ -279,7 +279,7 @@ class Chrome:
                 self._home_tmpdir.cleanup()
             except:
                 self.logger.error(
-                        "exception deleting %s", self._home_tmpdir,
+                        'exception deleting %s', self._home_tmpdir,
                         exc_info=True)
         finally:
             self._out_reader_thread.join()
diff --git a/brozzler/pywb.py b/brozzler/pywb.py
index 9b0a0f7..7b0b95a 100644
--- a/brozzler/pywb.py
+++ b/brozzler/pywb.py
@@ -70,7 +70,7 @@ class RethinkCDXSource(pywb.cdx.cdxsource.CDXSource):
                 'filename': record['filename'],
             }
             if record['warc_type'] != 'revisit':
-                blob['mime'] = record['content_type']
+                blob['mime'] = record['content_type'] or '-'
             else:
                 blob['mime'] = 'warc/revisit'
             # b'org,archive)/ 20160427215530 {"url": "https://archive.org/", "mime": "text/html", "status": "200", "digest": "VILUFXZD232SLUA6XROZQIMEVUPW6EIE", "length": "16001", "offset": "90144", "filename": "ARCHIVEIT-261-ONE_TIME-JOB209607-20160427215508135-00000.warc.gz"}'
diff --git a/setup.py b/setup.py
index 2fd868a..7fd25c6 100644
--- a/setup.py
+++ b/setup.py
@@ -32,7 +32,7 @@ def find_package_data(package):
 
 setuptools.setup(
         name='brozzler',
-        version='1.1b8.dev135',
+        version='1.1b8.dev137',
         description='Distributed web crawling with browsers',
         url='https://github.com/internetarchive/brozzler',
         author='Noah Levitt',
diff --git a/tests/test_units.py b/tests/test_units.py
index acd5fd0..f8042f0 100644
--- a/tests/test_units.py
+++ b/tests/test_units.py
@@ -25,6 +25,7 @@ import brozzler
 import brozzler.chrome
 import socket
 import logging
+import psutil
 
 @pytest.fixture(scope='module')
 def httpd(request):