diff --git a/Framework/Crystal/src/ClusterRegister.cpp b/Framework/Crystal/src/ClusterRegister.cpp
index 8a986ee21dd9234332bfa9655f959cdba2a705ea..a259ba620906bed8aca192c01888e0e42d480eeb 100644
--- a/Framework/Crystal/src/ClusterRegister.cpp
+++ b/Framework/Crystal/src/ClusterRegister.cpp
@@ -3,6 +3,7 @@
 #include "MantidCrystal/CompositeCluster.h"
 #include <boost/make_shared.hpp>
 #include <boost/functional/hash.hpp>
+#include <set>
 
 namespace {
 template <typename T> std::pair<T, T> ordered_pair(const T &a, const T &b) {