diff --git a/python/dune/perftool/options.py b/python/dune/perftool/options.py
index 5ba55655bf43d6746495fec4db87c2e488bc724e..3589f773f15c5002d452accbd242ebc3d6c5a96b 100644
--- a/python/dune/perftool/options.py
+++ b/python/dune/perftool/options.py
@@ -16,7 +16,7 @@ class PerftoolOption(ImmutableRecord):
                  _type=type(None),
                  ):
         _type = type(default)
-        if _type is type(None):
+        if issubclass(_type, type(None)):
             _type = str
         ImmutableRecord.__init__(self,
                                  helpstr=helpstr,
@@ -127,7 +127,7 @@ def set_option(key, value):
     any other options.
     """
     global _options
-    _options = process_options(_options).copy(**{key:value})
+    _options = process_options(_options).copy(**{key: value})
 
 
 def get_option(key):
diff --git a/python/dune/perftool/sumfact/permutation.py b/python/dune/perftool/sumfact/permutation.py
index 34d322989042f1dd321ab80e850fe3a3a052cdaa..a377be6671c8b3fc5a98685205329c85948db1be 100644
--- a/python/dune/perftool/sumfact/permutation.py
+++ b/python/dune/perftool/sumfact/permutation.py
@@ -2,7 +2,7 @@
 
 # TODO!
 # * get rid of the underscores in names
-# * Pass the entire kernel object into the strategy thing 
+# * Pass the entire kernel object into the strategy thing
 
 import itertools
 
@@ -83,4 +83,4 @@ def _permute_backward(t, perm):
     tmp = [None] * len(t)
     for i, pos in enumerate(perm):
         tmp[pos] = t[i]
-    return tuple(tmp)
\ No newline at end of file
+    return tuple(tmp)
diff --git a/python/dune/perftool/sumfact/vectorization.py b/python/dune/perftool/sumfact/vectorization.py
index 7c3cfdd8deb991fe3b2636c0606e71e4d06ceede..c56bf97c7b9bc2cd6e8ec3048b9db8cd29a39dd2 100644
--- a/python/dune/perftool/sumfact/vectorization.py
+++ b/python/dune/perftool/sumfact/vectorization.py
@@ -117,4 +117,3 @@ def decide_vectorization_strategy():
         import itertools as it
         for restriction in it.product(res, res):
             decide_stage_vectorization_strategy(sumfacts, 3, restriction)
-