diff --git a/cpp/core/src/zxing/Binarizer.cpp b/cpp/core/src/zxing/Binarizer.cpp
index adaab0556..190138291 100644
--- a/cpp/core/src/zxing/Binarizer.cpp
+++ b/cpp/core/src/zxing/Binarizer.cpp
@@ -23,15 +23,17 @@
 
 namespace zxing {
 	
-	Binarizer::Binarizer(Ref<LuminanceSource> source) : source_(source), array_(NULL), matrix_(NULL) {
+	Binarizer::Binarizer(Ref<LuminanceSource> source) : source_(source), array_(NULL), matrix_(NULL), cached_y_(-1) {
 	}
 	
 	Binarizer::~Binarizer() {
 	}
 	
 	Ref<BitArray> Binarizer::getBlackRow(int y, Ref<BitArray> row){
-		if (array_ == NULL)
+		if (array_ == NULL && cached_y_ != y) {
 			array_ = estimateBlackRow(y, row);
+			cached_y_ = y;
+		}
 		return array_;
 	}
 	
diff --git a/cpp/core/src/zxing/Binarizer.h b/cpp/core/src/zxing/Binarizer.h
index 225ec7dce..694018d72 100644
--- a/cpp/core/src/zxing/Binarizer.h
+++ b/cpp/core/src/zxing/Binarizer.h
@@ -34,6 +34,7 @@ class Binarizer : public Counted {
   Ref<LuminanceSource> source_;
   Ref<BitArray> array_;
   Ref<BitMatrix> matrix_;
+  int cached_y_;
 
  public:
   Binarizer(Ref<LuminanceSource> source);
diff --git a/cpp/core/src/zxing/BinaryBitmap.cpp b/cpp/core/src/zxing/BinaryBitmap.cpp
index c8fea36e4..ff79b55d5 100644
--- a/cpp/core/src/zxing/BinaryBitmap.cpp
+++ b/cpp/core/src/zxing/BinaryBitmap.cpp
@@ -23,7 +23,7 @@
 
 namespace zxing {
 	
-	BinaryBitmap::BinaryBitmap(Ref<Binarizer> binarizer) : bits_(NULL), array_bits_(NULL), binarizer_(binarizer) {
+	BinaryBitmap::BinaryBitmap(Ref<Binarizer> binarizer) : bits_(NULL), array_bits_(NULL), binarizer_(binarizer), cached_y_(-1) {
 		
 	}
 	
@@ -31,8 +31,9 @@ namespace zxing {
 	}
 	
 	Ref<BitArray> BinaryBitmap::getBlackRow(int y, Ref<BitArray> row) {
-		if (array_bits_ == NULL) {
+		if (array_bits_ == NULL && cached_y_ != y) {
 			array_bits_ = binarizer_->getBlackRow(y, row);
+			cached_y_ = y;
 		}
 		return array_bits_;
 	}
diff --git a/cpp/core/src/zxing/BinaryBitmap.h b/cpp/core/src/zxing/BinaryBitmap.h
index ecd9a8549..ddea910c1 100644
--- a/cpp/core/src/zxing/BinaryBitmap.h
+++ b/cpp/core/src/zxing/BinaryBitmap.h
@@ -33,6 +33,7 @@ namespace zxing {
 		Ref<BitMatrix> bits_;
 		Ref<BitArray> array_bits_;
 		Ref<Binarizer> binarizer_;
+		int cached_y_;
 		
 	public:
 		BinaryBitmap(Ref<Binarizer> binarizer);