diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5e1c5cc..791878c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -32,7 +32,9 @@
 - Fix an image inside another image's description: it flattens into the alt text, where it was
   refused.
 - Fix a cyclic document, in which an object holds itself: `adfToMarkdown` and `adfToPlainMarkdown`
-  refuse it as `not-an-adf-document` and `isAdfDocument` returns `false`, where all three hung.
+  refuse it as `not-an-adf-document` and `isAdfDocument` returns `false`, where all three hung. A
+  node or mark whose `attrs`, `content`, `marks`, `text` or `type` is not its own enumerable key is
+  refused alike, where it was read.
 
 ## 0.1.0
 
diff --git a/src/adf/document.test.ts b/src/adf/document.test.ts
index af13f46..1a876fb 100644
--- a/src/adf/document.test.ts
+++ b/src/adf/document.test.ts
@@ -83,7 +83,7 @@ test("reads a node's siblings as a walk rather than as one call's arguments", ()
   assert.equal(fault(wide), 'accepted')
 })
 
-test('refuses a node or an attribute value holding itself, and accepts one shared', () => {
+test('refuses an object holding itself or a key it does not own, and accepts one shared', () => {
   const holdsItself = 'an ADF document is a tree: an object in it holds itself'
   const paragraph: { content: unknown[]; type: string } = { content: [], type: 'paragraph' }
   paragraph.content.push(paragraph)
@@ -108,6 +108,14 @@ test('refuses a node or an attribute value holding itself, and accepts one share
   const link: Record<string, unknown> = Object.create({ attrs })
   link['type'] = 'link'
   assert.equal(fault({ content: [{ marks: [link], text: 'x', type: 'text' }], type: 'doc', version: 1 }), notANode)
+  const indexed: unknown[] = []
+  Object.defineProperty(indexed, 0, { value: indexed })
+  assert.equal(fault({ content: [{ attrs: { a: indexed }, type: 'paragraph' }], type: 'doc', version: 1 }), holdsItself)
+  const inheritedIndex: { content?: unknown[]; type: string } = { type: 'paragraph' }
+  const heirs: unknown[] = Object.setPrototypeOf([], [inheritedIndex])
+  heirs.length = 1
+  inheritedIndex.content = heirs
+  assert.equal(fault({ content: [inheritedIndex], type: 'doc', version: 1 }), holdsItself)
   const bold = { type: 'strong' }
   const text = { marks: [bold], text: 'x', type: 'text' }
   const shared = { content: [text, text], type: 'paragraph' }
diff --git a/src/adf/document.ts b/src/adf/document.ts
index 7c4060b..290258b 100644
--- a/src/adf/document.ts
+++ b/src/adf/document.ts
@@ -135,7 +135,7 @@ function holdsItself(root: object): boolean {
     if (onPath.has(entry.item)) return true
     ancestors.push(entry.item)
     onPath.add(entry.item)
-    for (const child of Object.values(entry.item)) if (typeof child === 'object' && child !== null) pending.push({ depth: entry.depth + 1, item: child })
+    for (const child of Array.isArray(entry.item) ? [...entry.item] : Object.values(entry.item)) if (typeof child === 'object' && child !== null) pending.push({ depth: entry.depth + 1, item: child })
   }
   return false
 }
@@ -219,7 +219,7 @@ function extraKey(value: Record<string, unknown>, keys: readonly string[]): stri
   return Object.keys(value).find((key) => !keys.includes(key))
 }
 
-// holdsItself walks own enumerable keys alone, so a guard reading an inherited one could walk a cycle forever.
+// holdsItself walks own enumerable keys alone, so a guard reading any other key could walk a cycle forever.
 function ownsWhatItHolds(value: Record<string, unknown>, keys: readonly string[]): boolean {
   return keys.every((key) => !(key in value) || Object.prototype.propertyIsEnumerable.call(value, key))
 }