diff --git a/contrib/moses2/PhraseBased/Manager.cpp b/contrib/moses2/PhraseBased/Manager.cpp
index 7436b967a..7b62c5741 100644
--- a/contrib/moses2/PhraseBased/Manager.cpp
+++ b/contrib/moses2/PhraseBased/Manager.cpp
@@ -5,6 +5,8 @@
  *      Author: hieu
  */
 #include <boost/foreach.hpp>
+#include <boost/functional/hash.hpp>
+#include <boost/unordered_set.hpp>
 #include <vector>
 #include <sstream>
 #include "Manager.h"
@@ -218,7 +220,7 @@ std::string Manager::OutputNBest()
 {
 	arcLists.Sort();
 
-	set<string> distinctHypos;
+	boost::unordered_set<size_t> distinctHypos;
 
 	TrellisPaths<TrellisPath> contenders;
 	m_search->AddInitialTrellisPaths(contenders);
@@ -227,7 +229,7 @@ std::string Manager::OutputNBest()
 
 	// MAIN LOOP
 	stringstream out;
-  Moses2::FixPrecision(out);
+	Moses2::FixPrecision(out);
 
 	size_t maxIter = system.options.nbest.nbest_size * system.options.nbest.factor;
 	size_t bestInd = 0;
@@ -243,8 +245,10 @@ std::string Manager::OutputNBest()
 		if (system.options.nbest.only_distinct) {
 			string tgtPhrase = path->OutputTargetPhrase(system);
 			//cerr << "tgtPhrase=" << tgtPhrase << endl;
+			boost::hash<std::string> string_hash;
+			size_t hash = string_hash(tgtPhrase);
 
-			if (distinctHypos.insert(tgtPhrase).second) {
+			if (distinctHypos.insert(hash).second) {
 				ok = true;
 			}
 		}
diff --git a/contrib/moses2/SCFG/KBestExtractor.cpp b/contrib/moses2/SCFG/KBestExtractor.cpp
index 6f7f4ed2d..4674023c3 100644
--- a/contrib/moses2/SCFG/KBestExtractor.cpp
+++ b/contrib/moses2/SCFG/KBestExtractor.cpp
@@ -24,7 +24,7 @@ namespace SCFG
 KBestExtractor::KBestExtractor(const SCFG::Manager &mgr)
 :m_mgr(mgr)
 {
-	set<string> distinctHypos;
+	boost::unordered_set<size_t> distinctHypos;
 
 	ArcLists &arcLists = mgr.arcLists;
 	const Stack &lastStack = mgr.GetStacks().GetLastStack();
@@ -53,8 +53,10 @@ KBestExtractor::KBestExtractor(const SCFG::Manager &mgr)
 		if (mgr.system.options.nbest.only_distinct) {
 			string tgtPhrase = path->Output();
 			//cerr << "tgtPhrase=" << tgtPhrase << endl;
+			boost::hash<std::string> string_hash;
+			size_t hash = string_hash(tgtPhrase);
 
-			if (distinctHypos.insert(tgtPhrase).second) {
+			if (distinctHypos.insert(hash).second) {
 				ok = true;
 			}
 		}