diff --git a/stix2/sdo.py b/stix2/sdo.py
index 9f2871e..8115b9d 100644
--- a/stix2/sdo.py
+++ b/stix2/sdo.py
@@ -7,8 +7,8 @@ from .common import COMMON_PROPERTIES
 from .observables import ObservableProperty
 from .other import KillChainPhase
 from .properties import (IDProperty, IntegerProperty, ListProperty,
-                         ReferenceProperty, StringProperty,
-                         TimestampProperty, TypeProperty)
+                         ReferenceProperty, StringProperty, TimestampProperty,
+                         TypeProperty)
 from .utils import NOW
 
 
diff --git a/stix2/test/test_properties.py b/stix2/test/test_properties.py
index 3a1446b..01daebf 100644
--- a/stix2/test/test_properties.py
+++ b/stix2/test/test_properties.py
@@ -5,10 +5,10 @@ from stix2.exceptions import AtLeastOnePropertyError, DictionaryKeyError
 from stix2.observables import EmailMIMEComponent, ExtensionsProperty
 from stix2.properties import (BinaryProperty, BooleanProperty,
                               DictionaryProperty, EmbeddedObjectProperty,
-                              EnumProperty, HashesProperty,
-                              HexProperty, IDProperty, IntegerProperty,
-                              ListProperty, Property, ReferenceProperty,
-                              StringProperty, TimestampProperty, TypeProperty)
+                              EnumProperty, HashesProperty, HexProperty,
+                              IDProperty, IntegerProperty, ListProperty,
+                              Property, ReferenceProperty, StringProperty,
+                              TimestampProperty, TypeProperty)
 
 from .constants import FAKE_TIME
 
diff --git a/tox.ini b/tox.ini
index 69ae434..b1265ec 100644
--- a/tox.ini
+++ b/tox.ini
@@ -30,7 +30,9 @@ max-line-length=160
 
 [testenv:isort-check]
 deps = isort
-commands = isort -rc stix2 examples -c -df
+commands =
+    isort -rc stix2 examples -df
+    isort -rc stix2 examples -c
 
 [travis]
 python =