diff --git a/flat_tree/__init__.py b/flat_tree/__init__.py
index 032afb0..3713d5b 100644
--- a/flat_tree/__init__.py
+++ b/flat_tree/__init__.py
@@ -10,6 +10,6 @@ except ImportError:
 
 
 try:
-    __version__ = pkg_resources.get_distribution('flat_tree').version
+    __version__ = pkg_resources.get_distribution("flat_tree").version
 except Exception:
-    __version__ = 'unknown'
+    __version__ = "unknown"
diff --git a/flat_tree/accessor.py b/flat_tree/accessor.py
index 76c9827..a122654 100644
--- a/flat_tree/accessor.py
+++ b/flat_tree/accessor.py
@@ -1,6 +1,6 @@
 """An accessor for navigating flat trees."""
 
-__all__ = ['FlatTreeAccessor']
+__all__ = ["FlatTreeAccessor"]
 
 from typing import List, Optional
 
@@ -155,7 +155,7 @@ class FlatTreeAccessor:
         :param index: The index of the root of the tree
         """
         if index & 1:
-            message = 'Roots only available for tree depth 0'
+            message = "Roots only available for tree depth 0"
             raise ValueError(message)
 
         roots: List[int] = []
diff --git a/flat_tree/iterator.py b/flat_tree/iterator.py
index 0be35bc..02a07a3 100644
--- a/flat_tree/iterator.py
+++ b/flat_tree/iterator.py
@@ -1,6 +1,6 @@
 """Stateful iterator for flat trees."""
 
-__all__ = ['FlatTreeIterator']
+__all__ = ["FlatTreeIterator"]
 
 import attr
 
diff --git a/test/test_version.py b/test/test_version.py
index 86d75af..c6d2688 100644
--- a/test/test_version.py
+++ b/test/test_version.py
@@ -2,9 +2,9 @@
 
 
 def test_version_fails_gracefully(mocker):
-    target = 'pkg_resources.get_distribution'
+    target = "pkg_resources.get_distribution"
     mocker.patch(target, side_effect=Exception())
 
     from flat_tree.__init__ import __version__
 
-    assert __version__ == 'unknown'
+    assert __version__ == "unknown"