diff --git a/mert/Scorer.cpp b/mert/Scorer.cpp
index ca36cb96f..e865aa766 100644
--- a/mert/Scorer.cpp
+++ b/mert/Scorer.cpp
@@ -4,6 +4,7 @@
 #include "Vocabulary.h"
 #include "Util.h"
 #include "Singleton.h"
+#include "PreProcessFilter.h"
 
 namespace {
 
diff --git a/mert/Scorer.h b/mert/Scorer.h
index 049e39fbd..d89097a6e 100644
--- a/mert/Scorer.h
+++ b/mert/Scorer.h
@@ -8,10 +8,10 @@
 #include <vector>
 #include "Types.h"
 #include "ScoreData.h"
-#include "PreProcessFilter.h"
 
 using namespace std;
 
+class PreProcessFilter;
 class ScoreStats;
 
 namespace mert {