diff --git a/src/game/level.gd b/src/game/level.gd
index e05f94d..243a138 100644
--- a/src/game/level.gd
+++ b/src/game/level.gd
@@ -9,6 +9,8 @@ const SAVE_PATH_FMT := "user://{0}.state.res"
 ## Human-readable name
 @export var pretty_name: String
 
+@export var version := 0
+
 
 func get_save_path() -> String:
 	return SAVE_PATH_FMT.format([id])
diff --git a/src/world/save_state.gd b/src/world/save_state.gd
index 33e11e5..d3a209f 100644
--- a/src/world/save_state.gd
+++ b/src/world/save_state.gd
@@ -1,17 +1,18 @@
 class_name SaveState extends Resource
 ## Serializable container for gameplay state.
 
-const CURRENT_VERSION := 0
+const CURRENT_VERSION := 1
 const PERSISTENT_GROUP := "Persistent"
 const SERIALIZE_METHOD := "serialize"
 const DESERIALIZE_METHOD := "deserialize"
 
-@export var save_version := CURRENT_VERSION
-
-@export var level_path: String
-
 @export var persistent_state: Dictionary[String, Dictionary] = {}
 
+@export_group("Compatibility Data")
+@export var save_version := CURRENT_VERSION
+@export var level_path: String
+@export var level_version := -1
+
 @export_group("WorldManager State")
 @export var grunk_tank_limit: int
 @export var mp3_player_unlocked: bool
@@ -28,14 +29,34 @@ static func node_key(node: Node, world: World) -> String:
 
 
 func load_to_world(world: World) -> void:
+	# Check save compatibility
+	if save_version != SaveState.CURRENT_VERSION:
+		push_warning(
+			"Save state version ",
+			save_version,
+			" is incompatible with the current game version ",
+			SaveState.CURRENT_VERSION
+		)
+		return
+
 	if level_path != world.current_level_scene.resource_path:
 		push_warning(
-			"This save is for ",
+			"Save state for level ",
 			level_path,
-			" but the loaded level is for ",
+			" is incompatible with the current level ",
 			world.current_level_scene.resource_path
 		)
+		return
 
+	if level_version != world.current_level.version:
+		push_warning(
+			"Save state for level version ",
+			level_version,
+			" is incompatible with the current level version ",
+			world.current_level.version
+		)
+
+	# Deserialize world state
 	world.manager.grunk_tank_limit = grunk_tank_limit
 	world.manager.mp3_player_unlocked = mp3_player_unlocked
 	world.manager.toothbrush_unlocked = toothbrush_unlocked
@@ -44,9 +65,8 @@ func load_to_world(world: World) -> void:
 	world.manager.grunk_vault = grunk_vault
 	world.manager.alert_level = alert_level
 
-	var persistent := world.get_tree().get_nodes_in_group(PERSISTENT_GROUP)
-
-	for node: Node in persistent:
+	# Deserialize persistent level nodes
+	for node: Node in world.get_tree().get_nodes_in_group(PERSISTENT_GROUP):
 		var key := SaveState.node_key(node, world)
 		if key in persistent_state:
 			# Node is in our persistent state, so load it with data.
@@ -59,8 +79,11 @@ func load_to_world(world: World) -> void:
 static func serialize(world: World) -> SaveState:
 	var save := SaveState.new()
 
+	# Serialize compatibility data
 	save.level_path = world.current_level_scene.resource_path
+	save.level_version = world.current_level.version
 
+	# Serialize world state
 	save.grunk_tank_limit = world.manager.grunk_tank_limit
 	save.mp3_player_unlocked = world.manager.mp3_player_unlocked
 	save.toothbrush_unlocked = world.manager.toothbrush_unlocked
@@ -69,11 +92,8 @@ static func serialize(world: World) -> SaveState:
 	save.grunk_vault = world.manager.grunk_vault
 	save.alert_level = world.manager.alert_level
 
-	# NOTE: I'm assuming that `persistent` will have the same order ever time the world is loaded.
-	# This may not be the case. If so, we need to find a different way to uniquely identify nodes.
-	var persistent := world.get_tree().get_nodes_in_group(PERSISTENT_GROUP)
-
-	for node: Node in persistent:
+	# Serialize persistent level nodes
+	for node: Node in world.get_tree().get_nodes_in_group(PERSISTENT_GROUP):
 		var key := SaveState.node_key(node, world)
 		var data: Dictionary = Callable(node, SERIALIZE_METHOD).call()
 		save.persistent_state[key] = data