diff --git a/.isort.cfg b/.isort.cfg
index db580a5..e409e00 100644
--- a/.isort.cfg
+++ b/.isort.cfg
@@ -1,6 +1,5 @@
 [settings]
 skip = workbench.py
-not_skip = __init__.py
 known_third_party =
     antlr4,
     dateutil,
diff --git a/setup.py b/setup.py
index ca63890..1c16e43 100644
--- a/setup.py
+++ b/setup.py
@@ -51,7 +51,7 @@ setup(
         'pytz',
         'requests',
         'simplejson',
-        'six',
+        'six>=1.13.0',
         'stix2-patterns',
     ],
     project_urls={
diff --git a/stix2/environment.py b/stix2/environment.py
index 4ba912c..5ba82e9 100644
--- a/stix2/environment.py
+++ b/stix2/environment.py
@@ -1,5 +1,4 @@
 """Python STIX2 Environment API."""
-
 import copy
 import logging
 import time
@@ -463,7 +462,7 @@ def partial_location_distance(lat1, long1, lat2, long2, threshold):
         float: Number between 0.0 and 1.0 depending on match.
 
     """
-    from haversine import haversine, Unit
+    from haversine import Unit, haversine
     distance = haversine((lat1, long1), (lat2, long2), unit=Unit.KILOMETERS)
     result = 1 - (distance / threshold)
     logger.debug(
diff --git a/tox.ini b/tox.ini
index 328c03a..857414f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -30,8 +30,8 @@ max-line-length = 160
 [testenv:isort-check]
 deps = isort
 commands =
-  isort -rc stix2 examples -df
-  isort -rc stix2 examples -c
+  isort stix2 examples --df
+  isort stix2 examples -c
 
 [testenv:packaging]
 deps =