diff --git a/km3io/tools.py b/km3io/tools.py
index 8def8ee42a080fb0b7669d6b45ce4f1e75a23fa4..16d81918378d3e6fe59baef03b51d96cc7f05181 100644
--- a/km3io/tools.py
+++ b/km3io/tools.py
@@ -57,8 +57,8 @@ class Branch:
     def _initialise_keys(self):
         """Create the keymap and instance attributes for branch keys"""
         # TODO: this could be a cached property
-        keys = set(k.decode('utf-8') for k in self._branch.keys()) - set(
-            self._mapper.exclude)
+        keys = set(k.decode('utf-8')
+                   for k in self._branch.keys()) - set(self._mapper.exclude)
         self._keymap = {
             **{self._mapper.attrparser(k): k
                for k in keys},
diff --git a/tests/test_tools.py b/tests/test_tools.py
index 4506869935a5a7f1331560744a6fb79c06e6e37f..bceb4a0b45fb77784274513b337d83e79c7de303 100644
--- a/tests/test_tools.py
+++ b/tests/test_tools.py
@@ -3,6 +3,7 @@
 import unittest
 from km3io.tools import _to_num, cached_property
 
+
 class TestToNum(unittest.TestCase):
     def test_to_num(self):
         self.assertEqual(10, _to_num("10"))