diff --git a/cpp/core/src/zxing/LuminanceSource.h b/cpp/core/src/zxing/LuminanceSource.h
index e23621ef9..d39f06f38 100644
--- a/cpp/core/src/zxing/LuminanceSource.h
+++ b/cpp/core/src/zxing/LuminanceSource.h
@@ -30,10 +30,10 @@ public:
   LuminanceSource();
   virtual ~LuminanceSource();
 
-  virtual int getWidth() = 0;
-  virtual int getHeight() = 0;
+  virtual int getWidth() const = 0;
+  virtual int getHeight() const = 0;
 
-  virtual unsigned char getPixel(int x, int y) = 0;
+  virtual unsigned char getPixel(int x, int y) const = 0;
   virtual unsigned char* copyMatrix();
 };