diff --git a/src/blitter/32bpp_anim_sse4.cpp b/src/blitter/32bpp_anim_sse4.cpp
--- a/src/blitter/32bpp_anim_sse4.cpp
+++ b/src/blitter/32bpp_anim_sse4.cpp
@@ -35,8 +35,7 @@ inline void Blitter_32bppSSE4_Anim::Draw
 {
 	const byte * const remap = bp->remap;
 	Colour *dst_line = (Colour *) bp->dst + bp->top * bp->pitch + bp->left;
-	assert(_screen.pitch == this->anim_buf_pitch); // precondition for translating 'bp->dst' into an 'anim_buf' offset below.
-	uint16 *anim_line = this->anim_buf + ((uint32 *)bp->dst - (uint32 *)_screen.dst_ptr) + bp->top * this->anim_buf_pitch + bp->left;
+	uint16 *anim_line = this->anim_buf + this->ScreenToAnimOffset((uint32 *)bp->dst) + bp->top * this->anim_buf_pitch + bp->left;
 	int effective_width = bp->width;
 
 	/* Find where to start reading in the source sprite. */