diff --git a/engine/billboard.go b/engine/billboard.go
index 7e0e5f5..02d9791 100644
--- a/engine/billboard.go
+++ b/engine/billboard.go
@@ -13,6 +13,7 @@ var _ interface {
 	Drawer
 	ParallaxScaler
 	Scanner
+	Transformer
 } = &Billboard{}
 
 func init() {
diff --git a/engine/walls.go b/engine/walls.go
index 7c7cb4c..4a1ec51 100644
--- a/engine/walls.go
+++ b/engine/walls.go
@@ -18,6 +18,8 @@ var (
 		Disabler
 		Hider
 		Prepper
+		Scanner
+		Transformer
 	} = &WallUnit{}
 )