diff --git a/src/blitter/32bpp_optimized.cpp b/src/blitter/32bpp_optimized.cpp
index c11a404010..ee3e05e9dc 100644
--- a/src/blitter/32bpp_optimized.cpp
+++ b/src/blitter/32bpp_optimized.cpp
@@ -337,6 +337,7 @@ Sprite *Blitter_32bppOptimized::Encode(SpriteLoader::Sprite *sprite, AllocatorPr
 	dest_sprite->y_offs = sprite->y_offs;
 
 	SpriteData *dst = (SpriteData *)dest_sprite->data;
+	memset(dst, 0, sizeof(*dst));
 
 	for (ZoomLevel z = zoom_min; z <= zoom_max; z++) {
 		dst->offset[z][0] = z == zoom_min ? 0 : lengths[z - 1][1] + dst->offset[z - 1][1];
diff --git a/src/blitter/8bpp_optimized.cpp b/src/blitter/8bpp_optimized.cpp
index acef6949ee..77fc36576e 100644
--- a/src/blitter/8bpp_optimized.cpp
+++ b/src/blitter/8bpp_optimized.cpp
@@ -141,6 +141,7 @@ Sprite *Blitter_8bppOptimized::Encode(SpriteLoader::Sprite *sprite, AllocatorPro
 	 * and the memory usage is quite low. */
 	static ReusableBuffer<byte> temp_buffer;
 	SpriteData *temp_dst = (SpriteData *)temp_buffer.Allocate(memory);
+	memset(temp_dst, 0, sizeof(*temp_dst));
 	byte *dst = temp_dst->data;
 
 	/* Make the sprites per zoom-level */