diff --git a/openmc/aggregate.py b/openmc/aggregate.py
index 908ca4b5c..70ce3685c 100644
--- a/openmc/aggregate.py
+++ b/openmc/aggregate.py
@@ -256,7 +256,7 @@ class AggregateFilter(object):
         if existing is None:
             clone = type(self).__new__(type(self))
             clone._type = self.type
-            clone._filter = self.aggregate_filter
+            clone._aggregate_filter = self.aggregate_filter
             clone._aggregate_op = self.aggregate_op
             clone._bins = self._bins
             clone._stride = self.stride
diff --git a/openmc/statepoint.py b/openmc/statepoint.py
index 76a14a80c..49ac43590 100644
--- a/openmc/statepoint.py
+++ b/openmc/statepoint.py
@@ -3,6 +3,7 @@ import re
 import numpy as np
 
 import openmc
+import openmc.checkvalue as cv
 
 if sys.version > '3':
     long = int