diff --git a/src/bin/bitsy-merge.rs b/src/bin/bitsy-merge.rs
index 1a6f47f..9ea139f 100644
--- a/src/bin/bitsy-merge.rs
+++ b/src/bin/bitsy-merge.rs
@@ -12,7 +12,7 @@ fn main() {
     let mut game_a = Game::from(fs::read_to_string(game_a).unwrap()).unwrap();
     let     game_b = Game::from(fs::read_to_string(game_b).unwrap()).unwrap();
 
-    game_a.merge(game_b);
+    game_a.merge(&game_b);
 
     fs::write(output, game_a.to_string())
         .expect("Failed to write output file");
diff --git a/src/game.rs b/src/game.rs
index 0f82964..7d9c157 100644
--- a/src/game.rs
+++ b/src/game.rs
@@ -314,7 +314,7 @@ impl Game {
     }
 
     // return? array of changes made? error/ok?
-    pub fn merge(&mut self, game: Game) {
+    pub fn merge(&mut self, game: &Game) {
         // ignore title, version, room format, room type, font, text direction
 
         let mut palette_id_changes:  HashMap<String, String> = HashMap::new();
@@ -942,7 +942,7 @@ mod test {
     fn merge() {
         // try merging two default games
         let mut game = crate::mock::game_default();
-        game.merge(crate::mock::game_default());
+        game.merge(&crate::mock::game_default());
 
         assert_eq!(game.room_ids(), vec!["0".to_string(), "1".to_string()]);
         assert_eq!(game.tile_ids(), vec!["a".to_string(), "1".to_string()]); // 0 is reserved
@@ -981,7 +981,7 @@ mod test {
         room.id = room_id.clone();
         sprite.room_id = Some(room_id.clone());
         game_b.add_sprite(sprite);
-        game_a.merge(game_b);
+        game_a.merge(&game_b);
         assert_eq!(game_a.get_sprite_by_id("2".to_string()).unwrap().room_id, Some(room_id));
     }