diff --git a/openmc/filter.py b/openmc/filter.py
index 6c059d66e..bc6b0bd35 100644
--- a/openmc/filter.py
+++ b/openmc/filter.py
@@ -1083,7 +1083,7 @@ class RealFilter(Filter):
             return np.allclose(self.bins, other.bins)
 
     def get_bin_index(self, filter_bin):
-        i = np.where(i = np.where(self.bins == filter_bin[1])[0]
+        i = np.where(self.bins == filter_bin[1])[0]
         if len(i) == 0:
             msg = 'Unable to get the bin index for Filter since "{0}" ' \
                   'is not one of the bins'.format(filter_bin)