diff --git a/package.json b/package.json
index f74582a7..ba9067cb 100644
--- a/package.json
+++ b/package.json
@@ -71,7 +71,8 @@
           "**/*.ts"
         ],
         "rules": {
-          "@typescript-eslint/ban-types": "off"
+          "@typescript-eslint/ban-types": "off",
+          "@typescript-eslint/consistent-type-definitions": "off"
         }
       }
     ],
diff --git a/packages/rehype-parse/index.d.ts b/packages/rehype-parse/index.d.ts
index 9daa1a06..4e34af21 100644
--- a/packages/rehype-parse/index.d.ts
+++ b/packages/rehype-parse/index.d.ts
@@ -17,3 +17,8 @@ export type {Options} from './lib/index.js'
  */
 declare const rehypeParse: Plugin<[(Options | null | undefined)?], string, Root>
 export default rehypeParse
+
+// Add custom settings supported when `rehype-parse` is added.
+declare module 'unified' {
+  interface Settings extends Options {}
+}
diff --git a/packages/rehype-parse/lib/index.js b/packages/rehype-parse/lib/index.js
index 5101e47d..6c0125d9 100644
--- a/packages/rehype-parse/lib/index.js
+++ b/packages/rehype-parse/lib/index.js
@@ -32,8 +32,7 @@ export default function rehypeParse(options) {
   /** @type {import('unified').Processor<Root>} */
   // @ts-expect-error: TS in JSDoc generates wrong types if `this` is typed regularly.
   const self = this
-  const processorSettings = /** @type {Options} */ (self.data('settings'))
-  const {emitParseErrors, ...settings} = {...processorSettings, ...options}
+  const {emitParseErrors, ...settings} = {...self.data('settings'), ...options}
 
   self.parser = parser
 
diff --git a/packages/rehype-stringify/index.d.ts b/packages/rehype-stringify/index.d.ts
index effed7e7..8b14a783 100644
--- a/packages/rehype-stringify/index.d.ts
+++ b/packages/rehype-stringify/index.d.ts
@@ -20,3 +20,8 @@ declare const rehypeStringify: Plugin<
   string
 >
 export default rehypeStringify
+
+// Add custom settings supported when `rehype-stringify` is added.
+declare module 'unified' {
+  interface Settings extends Options {}
+}
diff --git a/packages/rehype-stringify/lib/index.js b/packages/rehype-stringify/lib/index.js
index 5c1bb7f7..2060e7dc 100644
--- a/packages/rehype-stringify/lib/index.js
+++ b/packages/rehype-stringify/lib/index.js
@@ -18,8 +18,7 @@ export default function rehypeStringify(options) {
   /** @type {import('unified').Processor<undefined, undefined, undefined, Root, string>} */
   // @ts-expect-error: TS in JSDoc generates wrong types if `this` is typed regularly.
   const self = this
-  const processorSettings = /** @type {Options} */ (self.data('settings'))
-  const settings = {...processorSettings, ...options}
+  const settings = {...self.data('settings'), ...options}
 
   self.compiler = compiler
 
diff --git a/test/api.js b/test/api.js
index 2af1781a..5f296e2a 100644
--- a/test/api.js
+++ b/test/api.js
@@ -1,4 +1,5 @@
 /**
+ * @typedef {import('unified').Settings} Settings
  * @typedef {import('hast').Root} Root
  */
 
@@ -78,7 +79,6 @@ test('rehype', async function (t) {
     async function () {
       assert.deepEqual(
         unified()
-          // @ts-expect-error: to do: type `settings`.
           .data('settings', {fragment: true})
           .use(rehypeParse, {fragment: false})
           .use(rehypeStringify)
@@ -94,7 +94,6 @@ test('rehype', async function (t) {
     async function () {
       assert.deepEqual(
         unified()
-          // @ts-expect-error: to do: type `settings`.
           .data('settings', {quote: '"'})
           .use(rehypeParse, {fragment: true})
           .use(rehypeStringify, {quote: "'"})
@@ -187,8 +186,10 @@ test('rehype', async function (t) {
     'should throw when `tree` is not a valid node',
     async function () {
       assert.throws(function () {
-        // @ts-expect-error: unknown node.
-        unified().use(rehypeStringify).stringify({type: 'unicorn'})
+        unified()
+          .use(rehypeStringify)
+          // @ts-expect-error: check how an unknown node is handled.
+          .stringify({type: 'unicorn'})
       }, /unicorn/)
     }
   )
@@ -308,7 +309,6 @@ test('rehype', async function (t) {
     async function () {
       assert.deepEqual(
         rehype()
-          // @ts-expect-error: to do: type `settings`.
           .data('settings', {emitParseErrors: true})
           .processSync('<!doctypehtml>')
           .messages.map(String),
@@ -323,7 +323,6 @@ test('rehype', async function (t) {
       assert.deepEqual(
         rehype()
           .data('settings', {
-            // @ts-expect-error: to do: type `settings`.
             emitParseErrors: true,
             missingWhitespaceBeforeDoctypeName: false
           })
@@ -340,7 +339,6 @@ test('rehype', async function (t) {
       assert.deepEqual(
         rehype()
           .data('settings', {
-            // @ts-expect-error: to do: type `settings`.
             emitParseErrors: true,
             missingWhitespaceBeforeDoctypeName: true
           })
@@ -357,7 +355,6 @@ test('rehype', async function (t) {
       assert.deepEqual(
         rehype()
           .data('settings', {
-            // @ts-expect-error: to do: type `settings`.
             emitParseErrors: true,
             missingWhitespaceBeforeDoctypeName: 2
           })
@@ -373,7 +370,6 @@ test('rehype', async function (t) {
       assert.deepEqual(
         rehype()
           .data('settings', {
-            // @ts-expect-error: to do: type `settings`.
             emitParseErrors: true,
             missingWhitespaceBeforeDoctypeName: 1
           })
@@ -403,15 +399,15 @@ test('fixtures', async function (t) {
       const expectedTreeUrl = new URL('index.json', base)
       const expectedOutputUrl = new URL('result.html', base)
 
-      // To do: types of `Settings`.
-      /** @type {{fragment?: boolean, reprocess?: boolean}} */
-      let settings = {}
+      /** @type {Settings & {reprocess?: boolean | null | undefined}} */
+      let config = {}
 
       try {
-        settings = JSON.parse(String(await fs.readFile(configUrl)))
+        config = JSON.parse(String(await fs.readFile(configUrl)))
       } catch {}
 
-      // @ts-expect-error: To do: types of `Settings`.
+      const {reprocess, ...settings} = config
+
       const processor = rehype().data('settings', settings)
       const input = new VFile({
         basename: 'index.html',
@@ -449,9 +445,8 @@ test('fixtures', async function (t) {
       assert.deepEqual(actualTree, expectedTree)
       assert.equal(actualOutput, expectedOutput)
 
-      if (settings.reprocess !== false) {
+      if (reprocess !== false) {
         const reprocessedTree = rehype()
-          // @ts-expect-error: to do: type `settings`.
           .data('settings', settings)
           .parse(actualOutput)
         removePosition(actualTree)