diff --git a/mobile/mobile.go b/mobile/mobile.go
index eceed154f..e320127db 100644
--- a/mobile/mobile.go
+++ b/mobile/mobile.go
@@ -24,21 +24,7 @@ import (
 )
 
 // Game defines necessary functions for a mobile game.
-type Game interface {
-	// Update updates a game by one frame.
-	Update(*ebiten.Image) error
-
-	// Layout accepts a native view size in DP (device-independent pixels) and returns the game's logical screen
-	// size.
-	//
-	// The screen scale is automatically adjusted to fit the view.
-	//
-	// Layout is called at an initialization and whenever the view size is changed.
-	//
-	// You can return a fixed screen size if you don't care, or you can also return a calculated screen size
-	// adjusted with the given view size.
-	Layout(viewWidth, viewHeight int) (screenWidth, screenHeight int)
-}
+type Game = ebiten.Game
 
 // SetGame sets a mobile game.
 //
diff --git a/run.go b/run.go
index 2005b817f..988327927 100644
--- a/run.go
+++ b/run.go
@@ -24,6 +24,25 @@ import (
 
 var _ = __EBITEN_REQUIRES_GO_VERSION_1_12_OR_LATER__
 
+// Game defines necessary functions for a game.
+//
+// Note: This interface is not used anywhere yet.
+type Game interface {
+	// Update updates a game by one frame.
+	Update(*Image) error
+
+	// Layout accepts a native outside size in DP (device-independent pixels) and returns the game's logical
+	// screen size.
+	//
+	// The screen scale is automatically adjusted to fit the outside.
+	//
+	// Layout is called at an initialization and whenever the outside size is changed.
+	//
+	// You can return a fixed screen size if you don't care, or you can also return a calculated screen size
+	// adjusted with the given outside size.
+	Layout(outsideWidth, outsideHeight int) (screenWidth, screenHeight int)
+}
+
 // TPS represents a default ticks per second, that represents how many times game updating happens in a second.
 const DefaultTPS = 60