diff --git a/src/blitter/32bpp_simple.hpp b/src/blitter/32bpp_simple.hpp
--- a/src/blitter/32bpp_simple.hpp
+++ b/src/blitter/32bpp_simple.hpp
@@ -28,7 +28,7 @@ class Blitter_32bppSimple : public Blitt
 public:
 	/* virtual */ void Draw(Blitter::BlitterParams *bp, BlitterMode mode, ZoomLevel zoom);
 	/* virtual */ void DrawColourMappingRect(void *dst, int width, int height, PaletteID pal);
-	/* virtual */ Sprite *Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator);
+	/* virtual */ Sprite *Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator);
 
 	/* virtual */ const char *GetName() { return "32bpp-simple"; }
 };