diff --git a/index.js b/index.js
index 6926d44..1718b93 100644
--- a/index.js
+++ b/index.js
@@ -21,7 +21,7 @@ function iteratorFactory(callback) {
       throw new Error('Missing children in `parent` for `modifier`')
     }
 
-    return iterate(children, callback, parent)
+    iterate(children, callback, parent)
   }
 }
 
diff --git a/package.json b/package.json
index 800e901..e8b05d8 100644
--- a/package.json
+++ b/package.json
@@ -21,22 +21,27 @@
   },
   "author": "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)",
   "contributors": [
-    "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)"
+    "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)",
+    "Merlijn Vos <merlijn@soverin.net>"
   ],
   "files": [
-    "index.js"
+    "index.js",
+    "types/index.d.ts"
   ],
+  "types": "types/index.d.ts",
   "dependencies": {
     "array-iterate": "^1.0.0"
   },
   "devDependencies": {
     "browserify": "^16.0.0",
+    "dtslint": "^3.3.0",
     "nyc": "^15.0.0",
     "prettier": "^1.0.0",
     "remark-cli": "^7.0.0",
     "remark-preset-wooorm": "^6.0.0",
     "tape": "^4.0.0",
     "tinyify": "^2.0.0",
+    "unified": "^8.4.2",
     "xo": "^0.26.0"
   },
   "scripts": {
@@ -46,7 +51,8 @@
     "build": "npm run build-bundle && npm run build-mangle",
     "test-api": "node test",
     "test-coverage": "nyc --reporter lcov tape test.js",
-    "test": "npm run format && npm run build && npm run test-coverage"
+    "test-types": "dtslint types",
+    "test": "npm run format && npm run build && npm run test-coverage && npm run test-types"
   },
   "prettier": {
     "tabWidth": 2,
diff --git a/types/index.d.ts b/types/index.d.ts
new file mode 100644
index 0000000..ec6473a
--- /dev/null
+++ b/types/index.d.ts
@@ -0,0 +1,25 @@
+// TypeScript Version: 3.5
+
+import {Node, Parent} from 'unist'
+
+declare namespace unistUtilModifyChildren {
+  type Modifier = (
+    node: Node,
+    index: number,
+    parent: Parent
+  ) => number | void
+
+  type Modify = (tree: Node) => void
+}
+
+/**
+ * unist utility to modify direct children of a parent.
+ *
+ * @param callback modifier function that (optionally) returns a next position (number) to iterate.
+ * @returns callback to be used on the tree.
+ */
+declare function unistUtilModifyChildren(
+  modifier: unistUtilModifyChildren.Modifier
+): unistUtilModifyChildren.Modify
+
+export = unistUtilModifyChildren
diff --git a/types/tsconfig.json b/types/tsconfig.json
new file mode 100644
index 0000000..c09a33a
--- /dev/null
+++ b/types/tsconfig.json
@@ -0,0 +1,10 @@
+{
+  "compilerOptions": {
+    "lib": ["es2015"],
+    "strict": true,
+    "baseUrl": ".",
+    "paths": {
+      "unist-util-modify-children": ["index.d.ts"]
+    }
+  }
+}
diff --git a/types/tslint.json b/types/tslint.json
new file mode 100644
index 0000000..9d87fc0
--- /dev/null
+++ b/types/tslint.json
@@ -0,0 +1,8 @@
+
+{
+  "extends": "dtslint/dtslint.json",
+  "rules": {
+    "whitespace": false,
+    "semicolon": false
+  }
+}
diff --git a/types/unist-util-modify-children-test.ts b/types/unist-util-modify-children-test.ts
new file mode 100644
index 0000000..bd39114
--- /dev/null
+++ b/types/unist-util-modify-children-test.ts
@@ -0,0 +1,43 @@
+import {Node} from 'unist'
+
+import unified = require('unified')
+
+import * as modifyChildren from 'unist-util-modify-children'
+
+const node: Node = {
+  type: 'root',
+  children: [
+    {type: 'leaf', value: '1'},
+    {type: 'leaf', children: [{type: 'leaf', value: '2'}]},
+    {type: 'leaf', value: '3'}
+  ]
+}
+
+// $ExpectType Modify
+modifyChildren((node, index) => index + 1)
+
+// $ExpectType Modify
+modifyChildren(() => {})
+
+// $ExpectError
+modifyChildren(() => '')
+
+// $ExpectType void
+modifyChildren((node, index) => index + 1)(node)
+
+// Usable in unified transform
+unified().use(() => tree => {
+  const modify = modifyChildren((node, index, parent) => {
+    if (node.type === 'node') {
+      parent.children.splice(index, 1, {
+        type: 'subtree',
+        children: node.children
+      })
+      return index + 1
+    }
+  })
+
+  modify(tree)
+
+  return tree
+})