diff --git a/src/Rev2/Compatibility/System.cs b/src/Rev2/Compatibility/System.cs
index d4ddb89..71233dc 100644
--- a/src/Rev2/Compatibility/System.cs
+++ b/src/Rev2/Compatibility/System.cs
@@ -2,11 +2,13 @@
 
 namespace MoonTools.ECS.Rev2.Compatibility;
 
-public class System : Manipulator
+public abstract class System : Manipulator
 {
 	public FilterBuilder FilterBuilder => World.FilterBuilder;
 
-	public System(World world) : base(world) { }
+	protected System(World world) : base(world) { }
+
+	public abstract void Update();
 
 	protected ReadOnlySpan<T> ReadMessages<T>() where T : unmanaged => World.ReadMessages<T>();
 	protected T ReadMessage<T>() where T : unmanaged => World.ReadMessage<T>();