diff --git a/src/gfx.cpp b/src/gfx.cpp
--- a/src/gfx.cpp
+++ b/src/gfx.cpp
@@ -1132,7 +1132,7 @@ static void GfxMainBlitter(const Sprite 
 		void *clicked = _newgrf_debug_sprite_picker.clicked_pixel;
 
 		if (topleft <= clicked && clicked <= bottomright) {
-			uint offset = (((size_t)clicked - (size_t)topleft) % bp.pitch) / blitter->GetBytesPerPixel();
+			uint offset = (((size_t)clicked - (size_t)topleft) / blitter->GetBytesPerPixel()) % bp.pitch;
 			if (offset < (uint)bp.width) {
 				_newgrf_debug_sprite_picker.sprites.Include(sprite_id);
 			}