diff --git a/src/blitter/32bpp_simple.cpp b/src/blitter/32bpp_simple.cpp
--- a/src/blitter/32bpp_simple.cpp
+++ b/src/blitter/32bpp_simple.cpp
@@ -92,7 +92,7 @@ void Blitter_32bppSimple::DrawColourMapp
 	DEBUG(misc, 0, "32bpp blitter doesn't know how to draw this colour table ('%d')", pal);
 }
 
-Sprite *Blitter_32bppSimple::Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
+Sprite *Blitter_32bppSimple::Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
 {
 	Blitter_32bppSimple::Pixel *dst;
 	Sprite *dest_sprite = (Sprite *)allocator(sizeof(*dest_sprite) + sprite->height * sprite->width * sizeof(*dst));