diff --git a/util/TweenChannel.gd b/util/TweenChannel.gd
index ad727c0..6fe7ca1 100644
--- a/util/TweenChannel.gd
+++ b/util/TweenChannel.gd
@@ -70,9 +70,10 @@ func create_tween(target: Variant) -> Tween:
 ##
 ## The given tween must have been created with self.create_tween.
 func sync(what: Tween) -> void:
-	var last_terminated: Tween = null
-	while last_terminated != what:
-		last_terminated = await terminated
+	if what and what.is_valid():
+		var last_terminated: Tween = null
+		while last_terminated != what:
+			last_terminated = await terminated
 
 ## Yields until the given tween is invalid and then cleans up bookkeeping.
 ##