diff --git a/mert/BleuDocScorer.cpp b/mert/BleuDocScorer.cpp
index 48c17ee96..d71c5171d 100644
--- a/mert/BleuDocScorer.cpp
+++ b/mert/BleuDocScorer.cpp
@@ -174,7 +174,7 @@ statscore_t BleuDocScorer::calculateScore(const vector<int>& comps) const
   UTIL_THROW_IF(comps.size() != kBleuNgramOrder * 2 + 1, util::Exception, "Error");
 
   float logbleu = 0.0;
-  for (int i = 0; i < kBleuNgramOrder; ++i) {
+  for (size_t i = 0; i < kBleuNgramOrder; ++i) {
     if (comps[2*i] == 0) {
       return 0.0;
     }
diff --git a/mert/BleuDocScorer.h b/mert/BleuDocScorer.h
index 9677410f8..d27088254 100644
--- a/mert/BleuDocScorer.h
+++ b/mert/BleuDocScorer.h
@@ -1,5 +1,4 @@
-#ifndef MERT_BLEU_DOC_SCORER_H_
-#define MERT_BLEU_DOC_SCORER_H_
+#pragma once
 
 #include <ostream>
 #include <string>
@@ -64,4 +63,3 @@ private:
 
 }
 
-#endif  // MERT_BLEU_DOC_SCORER_H_
diff --git a/mert/BleuScorer.cpp b/mert/BleuScorer.cpp
index 13a472447..dc926054f 100644
--- a/mert/BleuScorer.cpp
+++ b/mert/BleuScorer.cpp
@@ -99,9 +99,8 @@ void BleuScorer::setReferenceFiles(const vector<string>& referenceFiles)
     TRACE_ERR("Loading reference from " << referenceFiles[i] << endl);
 
     ifstream ifs(referenceFiles[i].c_str());
-    UTIL_THROW_IF2(!ifs, "Cannot open " << referenceFiles[i]);
     if (!OpenReferenceStream(&ifs, i)) {
-      UTIL_THROW2("Unable to open " + referenceFiles[i]);
+      UTIL_THROW2("Cannot open " + referenceFiles[i]);
     }
   }
 }
@@ -152,13 +151,26 @@ void BleuScorer::ProcessReferenceLine(const std::string& line, Reference* ref) c
     ref->push_back(length);
 }
 
+bool BleuScorer::GetNextReferenceFromStreams(std::vector<boost::shared_ptr<std::ifstream> >& referenceStreams, Reference& ref) const
+{
+  for (vector<boost::shared_ptr<ifstream> >::iterator ifs=referenceStreams.begin(); ifs!=referenceStreams.end(); ++ifs)
+  {
+    if (!(*ifs)) return false;
+    string line;
+    if (!getline(**ifs, line)) return false;
+    line = preprocessSentence(line);
+    ProcessReferenceLine(line, &ref);
+  }
+  return true;
+}
+
 void BleuScorer::prepareStats(size_t sid, const string& text, ScoreStats& entry)
 {
   UTIL_THROW_IF2(sid >= m_references.size(), "Sentence id (" << sid << ") not found in reference set");
-  CalcBleuStats(m_references[sid], text, entry);
+  CalcBleuStats(*(m_references[sid]), text, entry);
 }
 
-void BleuScorer::CalcBleuStats(const Reference* ref, const std::string& text, ScoreStats& entry) const
+void BleuScorer::CalcBleuStats(const Reference& ref, const std::string& text, ScoreStats& entry) const
 {
   NgramCounts testcounts;
   // stats for this line
@@ -177,7 +189,7 @@ void BleuScorer::CalcBleuStats(const Reference* ref, const std::string& text, Sc
     NgramCounts::Value correct = 0;
 
     NgramCounts::Value v = 0;
-    if (ref->get_counts()->Lookup(testcounts_it->first, &v)) {
+    if (ref.get_counts()->Lookup(testcounts_it->first, &v)) {
       correct = min(v, guess);
     }
     stats[len * 2 - 2] += correct;
@@ -207,17 +219,17 @@ statscore_t BleuScorer::calculateScore(const vector<ScoreStatsType>& comps) cons
   return exp(logbleu);
 }
 
-int BleuScorer::CalcReferenceLength(const Reference* ref, std::size_t length) const
+int BleuScorer::CalcReferenceLength(const Reference& ref, std::size_t length) const
 {
   switch (m_ref_length_type) {
   case AVERAGE:
-    return ref->CalcAverage();
+    return ref.CalcAverage();
     break;
   case CLOSEST:
-    return ref->CalcClosest(length);
+    return ref.CalcClosest(length);
     break;
   case SHORTEST:
-    return ref->CalcShortest();
+    return ref.CalcShortest();
     break;
   default:
     UTIL_THROW2("Unknown reference types");
diff --git a/mert/BleuScorer.h b/mert/BleuScorer.h
index e90915822..d7ee8e4e7 100644
--- a/mert/BleuScorer.h
+++ b/mert/BleuScorer.h
@@ -1,23 +1,23 @@
-#ifndef MERT_BLEU_SCORER_H_
-#define MERT_BLEU_SCORER_H_
+#pragma once
 
-#include <ostream>
+#include <fstream>
 #include <string>
 #include <vector>
 
-#include "Types.h"
+#include <boost/shared_ptr.hpp>
+
+#include "Ngram.h"
+#include "Reference.h"
+#include "ScopedVector.h"
 #include "ScoreData.h"
 #include "StatisticsBasedScorer.h"
-#include "ScopedVector.h"
+#include "Types.h"
 
 namespace MosesTuning
 {
 
 const size_t kBleuNgramOrder = 4;
 
-class NgramCounts;
-class Reference;
-
 /**
  * Bleu scoring
  */
@@ -42,9 +42,9 @@ public:
     return 2 * kBleuNgramOrder + 1;
   }
 
-  void CalcBleuStats(const Reference* ref, const std::string& text, ScoreStats& entry) const;
+  void CalcBleuStats(const Reference& ref, const std::string& text, ScoreStats& entry) const;
 
-  int CalcReferenceLength(const Reference* ref, std::size_t length) const;
+  int CalcReferenceLength(const Reference& ref, std::size_t length) const;
 
   ReferenceLengthType GetReferenceLengthType() const {
     return m_ref_length_type;
@@ -65,7 +65,7 @@ public:
   /**
    * Count the ngrams of each type, up to the given length in the input line.
    */
-  std::size_t CountNgrams(const std::string& line, NgramCounts& counts, unsigned int n, bool is_testing=false) const;
+  size_t CountNgrams(const std::string& line, NgramCounts& counts, unsigned int n, bool is_testing=false) const;
 
   void DumpCounts(std::ostream* os, const NgramCounts& counts) const;
 
@@ -74,6 +74,8 @@ public:
 
   void ProcessReferenceLine(const std::string& line, Reference* ref) const;
 
+  bool GetNextReferenceFromStreams(std::vector<boost::shared_ptr<std::ifstream> >& referenceStreams, Reference& ref) const;
+
   //private:
 protected:
   ReferenceLengthType m_ref_length_type;
@@ -102,4 +104,3 @@ float sentenceLevelBackgroundBleu(const std::vector<float>& sent, const std::vec
 
 }
 
-#endif  // MERT_BLEU_SCORER_H_
diff --git a/mert/HopeFearDecoder.cpp b/mert/HopeFearDecoder.cpp
index 5288116d6..be9d8f2c9 100644
--- a/mert/HopeFearDecoder.cpp
+++ b/mert/HopeFearDecoder.cpp
@@ -98,7 +98,7 @@ void NbestHopeFearDecoder::HopeFear(
   size_t hope_index=0, fear_index=0, model_index=0;
   ValType hope_score=0, fear_score=0, model_score=0;
   for(size_t safe_loop=0; safe_loop<2; safe_loop++) {
-    ValType hope_bleu, hope_model;
+    ValType hope_bleu=0, hope_model=0;
     for(size_t i=0; i< train_->cur_size(); i++) {
       const MiraFeatureVector& vec=train_->featuresAt(i);
       ValType score = wv.score(vec);
diff --git a/mert/HopeFearDecoder.h b/mert/HopeFearDecoder.h
index 53c0e935d..73f0e97d9 100644
--- a/mert/HopeFearDecoder.h
+++ b/mert/HopeFearDecoder.h
@@ -16,8 +16,7 @@ You should have received a copy of the GNU Lesser General Public
 License along with this library; if not, write to the Free Software
 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 ***********************************************************************/
-#ifndef MERT_HOPEFEARDECODER_H
-#define MERT_HOPEFEARDECODER_H
+#pragma once
 
 #include <vector>
 
@@ -160,5 +159,3 @@ private:
 
 };
 
-#endif
-
diff --git a/mert/Ngram.h b/mert/Ngram.h
index 521dc4928..de2703605 100644
--- a/mert/Ngram.h
+++ b/mert/Ngram.h
@@ -1,5 +1,4 @@
-#ifndef MERT_NGRAM_H_
-#define MERT_NGRAM_H_
+#pragma once
 
 #include <vector>
 #include <string>
@@ -121,4 +120,3 @@ private:
 
 }
 
-#endif  // MERT_NGRAM_H_
diff --git a/mert/Reference.h b/mert/Reference.h
index 2c12f2ed7..a7878f3e7 100644
--- a/mert/Reference.h
+++ b/mert/Reference.h
@@ -59,6 +59,11 @@ public:
   int CalcClosest(std::size_t length) const;
   int CalcShortest() const;
 
+  void clear() {
+    m_length.clear();
+    m_counts->clear();
+  }
+
 private:
   NgramCounts* m_counts;
 
diff --git a/mert/Scorer.h b/mert/Scorer.h
index 4383c68f2..a08fc436d 100644
--- a/mert/Scorer.h
+++ b/mert/Scorer.h
@@ -1,5 +1,4 @@
-#ifndef MERT_SCORER_H_
-#define MERT_SCORER_H_
+#pragma once
 
 #include <iostream>
 #include <sstream>
@@ -236,4 +235,3 @@ inline float score_average(const statscores_t& scores, size_t start, size_t end)
 
 }
 
-#endif // MERT_SCORER_H_
diff --git a/mert/sentence-bleu-nbest.cpp b/mert/sentence-bleu-nbest.cpp
index 023e9faae..f869386e3 100644
--- a/mert/sentence-bleu-nbest.cpp
+++ b/mert/sentence-bleu-nbest.cpp
@@ -1,9 +1,14 @@
+#include <fstream>
 #include <iostream>
 #include <vector>
 #include <string>
 
+#include <boost/shared_ptr.hpp>
+
 #include "BleuScorer.h"
+#include "Reference.h"
 #include "moses/Util.h"
+#include "util/exception.hh"
 
 using namespace MosesTuning;
 
@@ -24,21 +29,40 @@ int main(int argc, char **argv)
   BleuScorer scorer(config);
   scorer.setFactors(factors);
   scorer.setFilter(filter);
-  scorer.setReferenceFiles(refFiles); // TODO: we don't need to load the whole reference corpus into memory (this can take gigabytes of RAM if done with millions of sentences)
 
-  // Loading sentences and preparing statistics
+  // initialize reference streams
+  std::vector<boost::shared_ptr<std::ifstream> > refStreams;
+  for (std::vector<std::string>::const_iterator refFile=refFiles.begin(); refFile!=refFiles.end(); ++refFile)
+  {
+    TRACE_ERR("Loading reference from " << *refFile << std::endl);
+    boost::shared_ptr<std::ifstream> ifs(new std::ifstream(refFile->c_str()));
+    UTIL_THROW_IF2(!ifs, "Cannot open " << *refFile);
+    refStreams.push_back(ifs);
+  }
+
+  // load sentences, preparing statistics, score
   std::string nbestLine;
+  int sid = -1;
+  Reference ref;
   while ( getline(std::cin, nbestLine) ) 
   {
     std::vector<std::string> items;
     Moses::TokenizeMultiCharSeparator(items, nbestLine, " ||| ");
-    size_t sid = Moses::Scan<size_t>(items[0]);
+    int sidCurrent = Moses::Scan<int>(items[0]);
 
+    if (sidCurrent != sid) {
+      ref.clear();
+      if (!scorer.GetNextReferenceFromStreams(refStreams, ref)) {
+        UTIL_THROW2("Missing references");
+      }
+      sid = sidCurrent;
+    }
     ScoreStats scoreStats;
-    scorer.prepareStats(sid, items[1], scoreStats);
+    scorer.CalcBleuStats(ref, items[1], scoreStats);
     std::vector<float> stats(scoreStats.getArray(), scoreStats.getArray() + scoreStats.size());
     std::cout << smoothedSentenceBleu(stats) << std::endl;
   }
 
   return 0;
 }
+
diff --git a/mert/sentence-bleu.cpp b/mert/sentence-bleu.cpp
index 425122c05..9bdab30d2 100644
--- a/mert/sentence-bleu.cpp
+++ b/mert/sentence-bleu.cpp
@@ -1,18 +1,26 @@
+#include <fstream>
 #include <iostream>
 #include <vector>
 #include <string>
 
+#include <boost/shared_ptr.hpp>
+
 #include "BleuScorer.h"
+#include "Reference.h"
+#include "moses/Util.h"
+#include "util/exception.hh"
 
 using namespace std;
 using namespace MosesTuning;
 
+
 int main(int argc, char **argv)
 {
   if (argc == 1) {
     cerr << "Usage: ./sentence-bleu ref1 [ref2 ...] < candidate > bleu-scores" << endl;
     return 1;
   }
+
   vector<string> refFiles(argv + 1, argv + argc);
 
   // TODO all of these are empty for now
@@ -23,15 +31,28 @@ int main(int argc, char **argv)
   BleuScorer scorer(config);
   scorer.setFactors(factors);
   scorer.setFilter(filter);
-  scorer.setReferenceFiles(refFiles); // TODO: we don't need to load the whole reference corpus into memory (this can take gigabytes of RAM if done with millions of sentences)
 
-  // Loading sentences and preparing statistics
+  // initialize reference streams
+  vector<boost::shared_ptr<ifstream> > refStreams;
+  for (vector<string>::const_iterator refFile=refFiles.begin(); refFile!=refFiles.end(); ++refFile)
+  {
+    TRACE_ERR("Loading reference from " << *refFile << endl);
+    boost::shared_ptr<ifstream> ifs(new ifstream(refFile->c_str()));
+    UTIL_THROW_IF2(!ifs, "Cannot open " << *refFile);
+    refStreams.push_back(ifs);
+  }
+
+  // load sentences, preparing statistics, score
   string hypothesisLine;
   size_t sid = 0;
   while (getline(std::cin, hypothesisLine)) 
   {
+    Reference ref;
+    if (!scorer.GetNextReferenceFromStreams(refStreams, ref)) {
+      UTIL_THROW2("Missing references");
+    }
     ScoreStats scoreStats;
-    scorer.prepareStats(sid, hypothesisLine, scoreStats);
+    scorer.CalcBleuStats(ref, hypothesisLine, scoreStats);
     vector<float> stats(scoreStats.getArray(), scoreStats.getArray() + scoreStats.size());
     std::cout << smoothedSentenceBleu(stats) << std::endl;
     ++sid;
@@ -39,3 +60,4 @@ int main(int argc, char **argv)
 
   return 0;
 }
+