diff --git a/mert/BleuScorer.cpp b/mert/BleuScorer.cpp
index d8f14c366..efa189aa1 100644
--- a/mert/BleuScorer.cpp
+++ b/mert/BleuScorer.cpp
@@ -4,7 +4,7 @@
 #include <cmath>
 #include <climits>
 #include <fstream>
-#include <iterator>
+#include <iostream>
 #include <stdexcept>
 #include "Util.h"
 
@@ -236,14 +236,21 @@ float BleuScorer::calculateScore(const vector<int>& comps) const
   return exp(logbleu);
 }
 
-void BleuScorer::dump_counts(const NgramCounts& counts) const {
-  for (NgramCounts::const_iterator i = counts.begin();
-       i != counts.end(); ++i) {
-    cerr << "(";
-    copy(i->first.begin(), i->first.end(), ostream_iterator<int>(cerr," "));
-    cerr << ") " << i->second << ", ";
+void BleuScorer::dump_counts(ostream* os,
+                             const NgramCounts& counts) const {
+  for (NgramCounts::const_iterator it = counts.begin();
+       it != counts.end(); ++it) {
+    *os << "(";
+    const NgramCounts::Key& keys = it->first;
+    for (size_t i = 0; i < keys.size(); ++i) {
+      if (i != 0) {
+        *os << " ";
+      }
+      *os << keys[i];
+    }
+    *os << ") : " << it->second << ", ";
   }
-  cerr << endl;
+  *os << endl;
 }
 
 void BleuScorer::CalcAverage(size_t sentence_id,
diff --git a/mert/BleuScorer.h b/mert/BleuScorer.h
index 6c1660fab..7ae19fa5f 100644
--- a/mert/BleuScorer.h
+++ b/mert/BleuScorer.h
@@ -1,7 +1,7 @@
 #ifndef MERT_BLEU_SCORER_H_
 #define MERT_BLEU_SCORER_H_
 
-#include <iostream>
+#include <ostream>
 #include <string>
 #include <vector>
 
@@ -45,7 +45,7 @@ private:
    */
   size_t countNgrams(const string& line, NgramCounts& counts, unsigned int n);
 
-  void dump_counts(const NgramCounts& counts) const;
+  void dump_counts(std::ostream* os, const NgramCounts& counts) const;
 
   // For calculating effective reference length.
   void CalcAverage(size_t sentence_id,