diff --git a/firanka/intervals.py b/firanka/intervals.py
index 36a3acf964ddffa4af87c286104a0d5d8a5bbc3f..e0e9ddc2ea131bd254d5e0ae5eae55bd660e941f 100644
--- a/firanka/intervals.py
+++ b/firanka/intervals.py
@@ -136,7 +136,7 @@ class Interval(object):
         """
         :type x: index or a Interval
         """
-        if isinstance(x, six.string_types) or isinstance(x, Interval):
+        if isinstance(x, str) or isinstance(x, Interval):
             return self._contains_interval(x)
         else:
             return self._contains_point(x)
diff --git a/firanka/series/interpolations.py b/firanka/series/interpolations.py
index 9e3a85b07c5c76d3a5d2ed495a920ec2260e8865..fc80ad6b98d7c819ca084cca40e7885d25d227e9 100644
--- a/firanka/series/interpolations.py
+++ b/firanka/series/interpolations.py
@@ -1,7 +1,3 @@
-
-
-import six
-
 from .base import DiscreteSeries, Series
 
 
@@ -38,7 +34,7 @@ class LinearInterpolationSeries(DiscreteSeries):
         if len(self.data) == 1:
             return super(LinearInterpolationSeries, self).__getitem__(item)
 
-        for i in six.moves.range(0, len(self.data) - 1):
+        for i in range(0, len(self.data) - 1):
             cur_i, cur_v = self.data[i]
             next_i, next_v = self.data[i + 1]