diff --git a/src/platform/mod.rs b/src/platform/mod.rs
index 454c649..4ed73c9 100644
--- a/src/platform/mod.rs
+++ b/src/platform/mod.rs
@@ -23,18 +23,23 @@ pub use self::winit::{WinitPlatform, WinitPlatformProvider};
 /// It handles starting and ticking the system, and provides a PlatformProvider
 /// to the system for screen/keyboard/etc. access.
 pub trait Platform {
+  /// Return a reference to a provider for systems to interact with this platform.
   fn provider(&self) -> Arc<dyn PlatformProvider>;
 }
 
 /// A platform which can be run synchronously.
 pub trait SyncPlatform: Platform {
+  /// Run the given system within this platform.
   fn run(&mut self, system: Box<dyn System>);
 }
 
 /// A platform which can be run asynchronously.
 #[async_trait(?Send)]
 pub trait AsyncPlatform: Platform {
+  /// Set up this platform for use.
   async fn setup(&mut self);
+
+  /// Execute one "step" of this platform. A step is implementation-defined.
   async fn tick(&mut self, system: &mut Box<dyn System>);
 }
 
diff --git a/src/platform/winit/mod.rs b/src/platform/winit/mod.rs
index 4ee4f0d..021c053 100644
--- a/src/platform/winit/mod.rs
+++ b/src/platform/winit/mod.rs
@@ -183,7 +183,12 @@ impl SyncPlatform for WinitPlatform {
               key_state.lock().unwrap().release(key);
             }
           },
-          WindowEvent::CloseRequested => *control_flow = ControlFlow::Exit,
+          WindowEvent::CloseRequested => {
+            if let Err(msg) = system.cleanup() {
+              println!("Error during cleanup: {}", msg);
+            }
+            *control_flow = ControlFlow::Exit;
+          }
           _ => (),
         },
         _ => (),
diff --git a/src/systems/mod.rs b/src/systems/mod.rs
index fe9c605..79b2f61 100644
--- a/src/systems/mod.rs
+++ b/src/systems/mod.rs
@@ -35,4 +35,9 @@ pub trait System {
 
   /// Render the current state of the system to the given framebuffer.
   fn render(&mut self, framebuffer: &mut [u8], window: WindowConfig);
+
+  /// Clean up any resources used by this system.
+  fn cleanup(&mut self) -> Result<(), &str> {
+    Ok(())
+  }
 }
diff --git a/src/wasm.rs b/src/wasm.rs
index 18326a1..cf6ef38 100644
--- a/src/wasm.rs
+++ b/src/wasm.rs
@@ -141,7 +141,7 @@ impl Noentiendo {
 
     let interval_id = {
       let system = system.clone();
-      let handler: Box<dyn FnMut() -> ()> = Box::new(move || {
+      let handler: Box<dyn FnMut()> = Box::new(move || {
         if platform_ready.get() {
           let platform = platform.clone();
           let system = system.clone();