diff --git a/qutebrowser/commands/utils.py b/qutebrowser/commands/utils.py
index b8b7968ee..339c404ce 100644
--- a/qutebrowser/commands/utils.py
+++ b/qutebrowser/commands/utils.py
@@ -45,13 +45,14 @@ class register:
 
     def __init__(self, instance=None, name=None, nargs=None, split_args=True,
                  hide=False, completion=None):
-        """Gets called on parse-time with the decorator arguments.
+        """Save decorator arguments.
+
+        Gets called on parse-time with the decorator arguments.
 
         Arguments:
             See class attributes.
 
         """
-
         self.name = name
         self.split_args = split_args
         self.hide = hide
@@ -60,7 +61,9 @@ class register:
         self.completion = completion
 
     def __call__(self, func):
-        """Gets called when a function should be decorated.
+        """Register the command before running the function.
+
+        Gets called when a function should be decorated.
 
         Doesn't actually decorate anything, but creates a Command object and
         registers it in the cmd_dict.
@@ -72,6 +75,7 @@ class register:
             The original function (unmodified).
 
         """
+        # FIXME: only register commands once
         names = []
         name = func.__name__.lower() if self.name is None else self.name
         if isinstance(name, str):
diff --git a/qutebrowser/config/conftypes.py b/qutebrowser/config/conftypes.py
index 2d305e441..0a48d121f 100644
--- a/qutebrowser/config/conftypes.py
+++ b/qutebrowser/config/conftypes.py
@@ -19,7 +19,9 @@
 
 
 class ValidationError(ValueError):
+
     """Exception raised when a value for a config type was invalid."""
+
     pass
 
 
diff --git a/qutebrowser/config/sections.py b/qutebrowser/config/sections.py
index 24826fbb8..f07af450c 100644
--- a/qutebrowser/config/sections.py
+++ b/qutebrowser/config/sections.py
@@ -180,6 +180,7 @@ class ValueList:
             valtype.validate(v)
             self.values[keytype.transform(k)] = valtype.transform(v)
 
+
 class SearchEngines(ValueList):
 
     """Search engine config section."""
diff --git a/qutebrowser/widgets/completion.py b/qutebrowser/widgets/completion.py
index 193be23a2..4137b1fa9 100644
--- a/qutebrowser/widgets/completion.py
+++ b/qutebrowser/widgets/completion.py
@@ -101,6 +101,7 @@ class CompletionView(QTreeView):
     def __init__(self, parent=None):
         super().__init__(parent)
         self._enabled = config.config.get('general', 'show_completion')
+        self._model = None
         self._completion_models = {
             'command': CompletionFilterModel(CommandCompletionModel(self)),
             'setting': CompletionFilterModel(SettingCompletionModel(self)),
@@ -155,6 +156,7 @@ class CompletionView(QTreeView):
         """Get a new completion model.
 
         parts: The command chunks to get a completion for.
+
         """
         if len(parts) == 1:
             return 'command'
diff --git a/run_checks.py b/run_checks.py
index 70749a3b7..cefba8757 100644
--- a/run_checks.py
+++ b/run_checks.py
@@ -60,6 +60,7 @@ options = {
             'no-init',
             'too-many-arguments',
             'too-few-public-methods',
+            'too-many-ancestors',
             # visual noise
             'locally-disabled',
         ],