diff --git a/lib/web/fetch/data-url.js b/lib/web/fetch/data-url.js
index ec4a8dc4e11..27ad7ae5924 100644
--- a/lib/web/fetch/data-url.js
+++ b/lib/web/fetch/data-url.js
@@ -8,12 +8,13 @@ const encoder = new TextEncoder()
 /**
  * @see https://mimesniff.spec.whatwg.org/#http-token-code-point
  */
-const HTTP_TOKEN_CODEPOINTS = /^[!#$%&'*+\-.^_|~A-Za-z0-9]+$/
-const HTTP_WHITESPACE_REGEX = /[\u000A\u000D\u0009\u0020]/ // eslint-disable-line
+const HTTP_TOKEN_CODEPOINTS = /^[-!#$%&'*+.^_|~A-Za-z0-9]+$/u
+const HTTP_WHITESPACE_REGEX = /[\u000A\u000D\u0009\u0020]/u // eslint-disable-line
+
 /**
  * @see https://mimesniff.spec.whatwg.org/#http-quoted-string-token-code-point
  */
-const HTTP_QUOTED_STRING_TOKENS = /^[\u0009\u0020-\u007E\u0080-\u00FF]+$/ // eslint-disable-line
+const HTTP_QUOTED_STRING_TOKENS = /^[\u0009\u0020-\u007E\u0080-\u00FF]+$/u // eslint-disable-line
 
 // https://fetch.spec.whatwg.org/#data-url-processor
 /** @param {URL} dataURL */
@@ -68,7 +69,7 @@ function dataURLProcessor (dataURL) {
   // 11. If mimeType ends with U+003B (;), followed by
   // zero or more U+0020 SPACE, followed by an ASCII
   // case-insensitive match for "base64", then:
-  if (/;(\u0020){0,}base64$/i.test(mimeType)) {
+  if (/;(?:\u0020*)base64$/ui.test(mimeType)) {
     // 1. Let stringBody be the isomorphic decode of body.
     const stringBody = isomorphicDecode(body)
 
@@ -86,7 +87,7 @@ function dataURLProcessor (dataURL) {
 
     // 5. Remove trailing U+0020 SPACE code points from mimeType,
     // if any.
-    mimeType = mimeType.replace(/(\u0020)+$/, '')
+    mimeType = mimeType.replace(/(\u0020+)$/u, '')
 
     // 6. Remove the last U+003B (;) code point from mimeType.
     mimeType = mimeType.slice(0, -1)
@@ -176,8 +177,9 @@ function percentDecode (input) {
   /** @type {Uint8Array} */
   const output = new Uint8Array(length)
   let j = 0
+  let i = 0
   // 2. For each byte byte in input:
-  for (let i = 0; i < length; ++i) {
+  while (i < length) {
     const byte = input[i]
 
     // 1. If byte is not 0x25 (%), then append byte to output.
@@ -205,6 +207,7 @@ function percentDecode (input) {
       // 3. Skip the next two bytes in input.
       i += 2
     }
+    ++i
   }
 
   // 3. Return output.
@@ -490,7 +493,7 @@ function serializeAMimeType (mimeType) {
     if (!HTTP_TOKEN_CODEPOINTS.test(value)) {
       // 1. Precede each occurrence of U+0022 (") or
       //    U+005C (\) in value with U+005C (\).
-      value = value.replace(/(\\|")/g, '\\$1')
+      value = value.replace(/[\\"]/ug, '\\$&')
 
       // 2. Prepend U+0022 (") to value.
       value = '"' + value