diff --git a/GPy/core/parameterization/index_operations.py b/GPy/core/parameterization/index_operations.py
index 01a13c8b..1e97f488 100644
--- a/GPy/core/parameterization/index_operations.py
+++ b/GPy/core/parameterization/index_operations.py
@@ -4,6 +4,7 @@
 import numpy
 from numpy.lib.function_base import vectorize
 from .lists_and_dicts import IntArrayDict
+from functools import reduce
 
 def extract_properties_to_index(index, props):
     prop_index = dict()