diff --git a/src/blitter/32bpp_optimized.cpp b/src/blitter/32bpp_optimized.cpp
--- a/src/blitter/32bpp_optimized.cpp
+++ b/src/blitter/32bpp_optimized.cpp
@@ -207,7 +207,7 @@ void Blitter_32bppOptimized::Draw(Blitte
 	}
 }
 
-Sprite *Blitter_32bppOptimized::Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
+Sprite *Blitter_32bppOptimized::Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
 {
 	/* streams of pixels (a, r, g, b channels)
 	 *
diff --git a/src/blitter/32bpp_optimized.hpp b/src/blitter/32bpp_optimized.hpp
--- a/src/blitter/32bpp_optimized.hpp
+++ b/src/blitter/32bpp_optimized.hpp
@@ -24,7 +24,7 @@ public:
 	};
 
 	/* virtual */ void Draw(Blitter::BlitterParams *bp, BlitterMode mode, ZoomLevel zoom);
-	/* virtual */ Sprite *Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator);
+	/* virtual */ Sprite *Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator);
 
 	/* virtual */ const char *GetName() { return "32bpp-optimized"; }
 
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));
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"; }
 };
diff --git a/src/blitter/8bpp_optimized.cpp b/src/blitter/8bpp_optimized.cpp
--- a/src/blitter/8bpp_optimized.cpp
+++ b/src/blitter/8bpp_optimized.cpp
@@ -112,7 +112,7 @@ void Blitter_8bppOptimized::Draw(Blitter
 	}
 }
 
-Sprite *Blitter_8bppOptimized::Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
+Sprite *Blitter_8bppOptimized::Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
 {
 	/* Make memory for all zoom-levels */
 	uint memory = sizeof(SpriteData);
diff --git a/src/blitter/8bpp_optimized.hpp b/src/blitter/8bpp_optimized.hpp
--- a/src/blitter/8bpp_optimized.hpp
+++ b/src/blitter/8bpp_optimized.hpp
@@ -25,7 +25,7 @@ public:
 	};
 
 	/* virtual */ void Draw(Blitter::BlitterParams *bp, BlitterMode mode, ZoomLevel zoom);
-	/* virtual */ Sprite *Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator);
+	/* virtual */ Sprite *Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator);
 
 	/* virtual */ const char *GetName() { return "8bpp-optimized"; }
 };
diff --git a/src/blitter/8bpp_simple.cpp b/src/blitter/8bpp_simple.cpp
--- a/src/blitter/8bpp_simple.cpp
+++ b/src/blitter/8bpp_simple.cpp
@@ -55,7 +55,7 @@ void Blitter_8bppSimple::Draw(Blitter::B
 	}
 }
 
-Sprite *Blitter_8bppSimple::Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
+Sprite *Blitter_8bppSimple::Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
 {
 	Sprite *dest_sprite;
 	dest_sprite = (Sprite *)allocator(sizeof(*dest_sprite) + sprite->height * sprite->width);
diff --git a/src/blitter/8bpp_simple.hpp b/src/blitter/8bpp_simple.hpp
--- a/src/blitter/8bpp_simple.hpp
+++ b/src/blitter/8bpp_simple.hpp
@@ -19,7 +19,7 @@
 class Blitter_8bppSimple FINAL : public Blitter_8bppBase {
 public:
 	/* virtual */ void Draw(Blitter::BlitterParams *bp, BlitterMode mode, ZoomLevel zoom);
-	/* virtual */ Sprite *Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator);
+	/* virtual */ Sprite *Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator);
 
 	/* virtual */ const char *GetName() { return "8bpp-simple"; }
 };
diff --git a/src/blitter/base.hpp b/src/blitter/base.hpp
--- a/src/blitter/base.hpp
+++ b/src/blitter/base.hpp
@@ -77,7 +77,7 @@ public:
 	/**
 	 * Convert a sprite from the loader to our own format.
 	 */
-	virtual Sprite *Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator) = 0;
+	virtual Sprite *Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator) = 0;
 
 	/**
 	 * Move the destination pointer the requested amount x and y, keeping in mind
diff --git a/src/blitter/null.cpp b/src/blitter/null.cpp
--- a/src/blitter/null.cpp
+++ b/src/blitter/null.cpp
@@ -15,7 +15,7 @@
 /** Instantiation of the null blitter factory. */
 static FBlitter_Null iFBlitter_Null;
 
-Sprite *Blitter_Null::Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
+Sprite *Blitter_Null::Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
 {
 	Sprite *dest_sprite;
 	dest_sprite = (Sprite *)allocator(sizeof(*dest_sprite));
diff --git a/src/blitter/null.hpp b/src/blitter/null.hpp
--- a/src/blitter/null.hpp
+++ b/src/blitter/null.hpp
@@ -20,7 +20,7 @@ public:
 	/* virtual */ uint8 GetScreenDepth() { return 0; }
 	/* 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 */ void *MoveTo(void *video, int x, int y) { return NULL; };
 	/* virtual */ void SetPixel(void *video, int x, int y, uint8 colour) {};
 	/* virtual */ void DrawRect(void *video, int width, int height, uint8 colour) {};