diff --git a/km3io/gseagen.py b/km3io/gseagen.py
index 5d4188feae932eaa353f7147470ea86a1bbb8433..d14502d6e1400f0b800164e2241b34badef4bb71 100644
--- a/km3io/gseagen.py
+++ b/km3io/gseagen.py
@@ -10,6 +10,7 @@ from .tools import cached_property
 
 class GSGReader(EventReader):
     """reader for gSeaGen ROOT files"""
+
     event_path = "Events"
     skip_keys = ["Header"]
 
diff --git a/km3io/rootio.py b/km3io/rootio.py
index c05b459338416fc1dae61e6cb0541b5ef90543ff..5c4e4de0bede7f414b336aeea6ee5551123e1c5f 100644
--- a/km3io/rootio.py
+++ b/km3io/rootio.py
@@ -10,6 +10,7 @@ import logging
 
 log = logging.getLogger("km3io.rootio")
 
+
 class EventReader:
     """reader for offline ROOT files"""
 
@@ -129,7 +130,9 @@ class EventReader:
         # indexing
         # TODO: maybe just propagate everything to awkward and let it deal
         # with the type?
-        if isinstance(key, (slice, int, np.int32, np.int64, list, np.ndarray, ak.Array)):
+        if isinstance(
+            key, (slice, int, np.int32, np.int64, list, np.ndarray, ak.Array)
+        ):
             if isinstance(key, (int, np.int32, np.int64)):
                 key = int(key)
             return self.__class__(
@@ -239,7 +242,11 @@ class EventReader:
             return 1
         else:
             # ignore the usual index magic and access `id` directly
-            return len(unfold_indices(self._fobj[self.event_path]["id"].array(), self._index_chain))
+            return len(
+                unfold_indices(
+                    self._fobj[self.event_path]["id"].array(), self._index_chain
+                )
+            )
 
     def __actual_len__(self):
         """The raw number of events without any indexing/slicing magic"""
diff --git a/tests/test_offline.py b/tests/test_offline.py
index 197105d17c380fbf3eb8eab8f07ce1ce9ee1f9fb..8e9e52e0a4d11ab0ed96922ad0e1507e77617c18 100644
--- a/tests/test_offline.py
+++ b/tests/test_offline.py
@@ -439,6 +439,7 @@ class TestBranchIndexingMagic(unittest.TestCase):
         # test selecting with a list
         self.assertEqual(3, len(self.events[ak.Array([0, 2, 3])]))
 
+
 class TestUsr(unittest.TestCase):
     def setUp(self):
         self.f = OFFLINE_USR