diff --git a/lib/web/fetch/headers.js b/lib/web/fetch/headers.js
index 39648ad1d02..44b1f52bb3f 100644
--- a/lib/web/fetch/headers.js
+++ b/lib/web/fetch/headers.js
@@ -15,14 +15,16 @@ const util = require('node:util')
 
 /**
  * @param {number} code
+ * @returns {code is (0x0a | 0x0d | 0x09 | 0x20)}
  */
 function isHTTPWhiteSpaceCharCode (code) {
-  return code === 0x00a || code === 0x00d || code === 0x009 || code === 0x020
+  return code === 0x0a || code === 0x0d || code === 0x09 || code === 0x20
 }
 
 /**
  * @see https://fetch.spec.whatwg.org/#concept-header-value-normalize
  * @param {string} potentialValue
+ * @returns {string}
  */
 function headerValueNormalize (potentialValue) {
   //  To normalize a byte sequence potentialValue, remove
@@ -36,6 +38,10 @@ function headerValueNormalize (potentialValue) {
   return i === 0 && j === potentialValue.length ? potentialValue : potentialValue.substring(i, j)
 }
 
+/**
+ * @param {Headers} headers
+ * @param {Array|Object} object
+ */
 function fill (headers, object) {
   // To fill a Headers object headers with a given object object, run these steps:
 
@@ -75,6 +81,9 @@ function fill (headers, object) {
 
 /**
  * @see https://fetch.spec.whatwg.org/#concept-headers-append
+ * @param {Headers} headers
+ * @param {string} name
+ * @param {string} value
  */
 function appendHeader (headers, name, value) {
   // 1. Normalize value.
@@ -417,8 +426,15 @@ class HeadersList {
 // https://fetch.spec.whatwg.org/#headers-class
 class Headers {
   #guard
+  /**
+   * @type {HeadersList}
+   */
   #headersList
 
+  /**
+   * @param {HeadersInit|Symbol} [init]
+   * @returns
+   */
   constructor (init = undefined) {
     if (init === kConstruct) {
       return
@@ -627,8 +643,12 @@ class Headers {
     return o.#headersList
   }
 
-  static setHeadersList (o, list) {
-    o.#headersList = list
+  /**
+   * @param {Headers} target
+   * @param {HeadersList} list
+   */
+  static setHeadersList (target, list) {
+    target.#headersList = list
   }
 }