diff --git a/src/mods/box/box.ts b/src/mods/box/box.ts
index 40b910d..80145f4 100644
--- a/src/mods/box/box.ts
+++ b/src/mods/box/box.ts
@@ -9,7 +9,11 @@ export class BoxMovedError extends Error {
   }
 }
 
-export class Box<T extends Disposable> implements Disposable {
+export interface MaybeDisposable {
+  [Symbol.dispose]?: () => void
+}
+
+export class Box<T extends MaybeDisposable> implements Disposable {
 
   moved = false
 
@@ -23,7 +27,7 @@ export class Box<T extends Disposable> implements Disposable {
   [Symbol.dispose]() {
     if (this.moved)
       return
-    this.inner[Symbol.dispose]()
+    this.inner[Symbol.dispose]?.()
   }
 
   /**
diff --git a/src/mods/copy/copy.ts b/src/mods/copy/copy.ts
index 3e21452..e4c948c 100644
--- a/src/mods/copy/copy.ts
+++ b/src/mods/copy/copy.ts
@@ -1,6 +1,6 @@
 export type BytesOrCopiable<N extends number = number> =
-  | Uint8Array & { length: N }
-  | Copiable<Uint8Array & { length: N }>
+  | Uint8Array & { readonly length: N }
+  | Copiable<Uint8Array & { readonly length: N }>
 
 /**
  * An object whose bytes can be copied
diff --git a/src/mods/slot/slot.ts b/src/mods/slot/slot.ts
index 667eb60..68928f2 100644
--- a/src/mods/slot/slot.ts
+++ b/src/mods/slot/slot.ts
@@ -1,14 +1,16 @@
+import { MaybeDisposable } from "index.js"
+
 /**
  * A disposable whose reference can change
  */
-export class Slot<T extends Disposable> implements Disposable {
+export class Slot<T extends MaybeDisposable> implements Disposable {
 
   constructor(
     public inner: T
   ) { }
 
   [Symbol.dispose]() {
-    this.inner[Symbol.dispose]()
+    this.inner[Symbol.dispose]?.()
   }
 
   static new<T extends Disposable>(inner: T) {