diff --git a/opencog/util/boost_ext/accumulators/statistics/geometric_mean_mirror.h b/opencog/util/boost_ext/accumulators/statistics/geometric_mean_mirror.h
index 70977b04cc..d6a5ec0d47 100644
--- a/opencog/util/boost_ext/accumulators/statistics/geometric_mean_mirror.h
+++ b/opencog/util/boost_ext/accumulators/statistics/geometric_mean_mirror.h
@@ -23,6 +23,8 @@
 #ifndef OPENCOG_UTIL_GEOMETRIC_MEAN_MIRROR
 #define OPENCOG_UTIL_GEOMETRIC_MEAN_MIRROR
 
+#include  <cmath>
+
 #include <boost/mpl/placeholders.hpp>
 #include <boost/accumulators/framework/accumulator_base.hpp>
 #include <boost/accumulators/framework/extractor.hpp>