diff --git a/.gitignore b/.gitignore
index c977c85..07e5d0a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
-.DS_Store
-*.d.ts
-*.log
 coverage/
 node_modules/
+.DS_Store
+test/**/*.d.ts
+index.d.ts
+*.log
 yarn.lock
diff --git a/complex-types.d.ts b/complex-types.d.ts
new file mode 100644
index 0000000..6c22a3c
--- /dev/null
+++ b/complex-types.d.ts
@@ -0,0 +1,11 @@
+import type {Literal} from 'nlcst'
+
+export interface Emoticon extends Literal {
+  type: 'EmoticonNode'
+}
+
+declare module 'nlcst' {
+  interface SentenceContentMap {
+    emoticon: Emoticon
+  }
+}
diff --git a/index.js b/index.js
index 0c6e8c1..cd8ab84 100644
--- a/index.js
+++ b/index.js
@@ -1,23 +1,28 @@
 /**
- * @typedef {import('unist').Node} Node
- * @typedef {import('unist').Parent} Parent
+ * @typedef {import('nlcst').Paragraph} Paragraph
+ * @typedef {import('nlcst').ParagraphContent} ParagraphContent
+ *
+ * @typedef {import('./complex-types').Emoticon} Emoticon
  */
 
 import {modifyChildren} from 'unist-util-modify-children'
 
-export const affixEmoticonModifier = modifyChildren(mergeAffixEmoticon)
+export const affixEmoticonModifier =
+  /** @type {(node: Paragraph) => void} */
+  // @ts-expect-error: To do: make types in `unist-util-modify-children` smart.
+  modifyChildren(mergeAffixEmoticon)
 
 /**
  * Merge emoticons into an `EmoticonNode`.
  *
- * @param {Node} node
+ * @param {ParagraphContent} node
  * @param {number} index
- * @param {Parent} ancestor
+ * @param {Paragraph} ancestor
  */
 function mergeAffixEmoticon(node, index, ancestor) {
   const previous = ancestor.children[index - 1]
 
-  if (index && parent(previous) && parent(node)) {
+  if (index && 'children' in previous && 'children' in node) {
     const children = node.children
     let childIndex = -1
 
@@ -43,11 +48,3 @@ function mergeAffixEmoticon(node, index, ancestor) {
     }
   }
 }
-
-/**
- * @param {Node} node
- * @returns {node is Parent}
- */
-function parent(node) {
-  return 'children' in node
-}
diff --git a/package.json b/package.json
index b1d0c94..9a930ac 100644
--- a/package.json
+++ b/package.json
@@ -27,10 +27,12 @@
   "main": "index.js",
   "types": "index.d.ts",
   "files": [
+    "complex-types.d.ts",
     "index.d.ts",
     "index.js"
   ],
   "dependencies": {
+    "@types/nlcst": "^1.0.0",
     "@types/unist": "^2.0.0",
     "unist-util-modify-children": "^3.0.0"
   },
@@ -55,7 +57,7 @@
   },
   "scripts": {
     "prepack": "npm run build && npm run format",
-    "build": "rimraf \"{test/**,}*.d.ts\" && tsc && type-coverage",
+    "build": "rimraf \"test/**/*.d.ts\" \"index.d.ts\" && tsc && type-coverage",
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
     "test-api": "node test/index.js",
     "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node test/index.js",
diff --git a/test/index.js b/test/index.js
index 59d1695..3174a36 100644
--- a/test/index.js
+++ b/test/index.js
@@ -1,5 +1,5 @@
 /**
- * @typedef {import('unist').Node} Node
+ * @typedef {import('nlcst').Root} Root
  */
 
 import fs from 'node:fs'
@@ -12,12 +12,12 @@ import {emoticonModifier} from 'nlcst-emoticon-modifier'
 import {removePosition} from 'unist-util-remove-position'
 import {affixEmoticonModifier} from '../index.js'
 
-/** @type {Node} */
+/** @type {Root} */
 const lollipop = JSON.parse(
   String(fs.readFileSync(path.join('test', 'fixtures', 'lollipop.json')))
 )
 
-/** @type {Node} */
+/** @type {Root} */
 const smile = JSON.parse(
   String(fs.readFileSync(path.join('test', 'fixtures', 'smile.json')))
 )