diff --git a/lib/web/fetch/body.js b/lib/web/fetch/body.js
index 464e7b50e5c..683a67400c8 100644
--- a/lib/web/fetch/body.js
+++ b/lib/web/fetch/body.js
@@ -3,8 +3,6 @@
 const util = require('../../core/util')
 const {
   ReadableStreamFrom,
-  isBlobLike,
-  isReadableStreamLike,
   readableStreamClose,
   createDeferredPromise,
   fullyReadBody,
@@ -44,7 +42,7 @@ function extractBody (object, keepalive = false) {
   // 2. If object is a ReadableStream object, then set stream to object.
   if (object instanceof ReadableStream) {
     stream = object
-  } else if (isBlobLike(object)) {
+  } else if (object instanceof Blob) {
     // 3. Otherwise, if object is a Blob object, set stream to the
     //    result of running object’s get stream.
     stream = object.stream()
@@ -67,7 +65,7 @@ function extractBody (object, keepalive = false) {
   }
 
   // 5. Assert: stream is a ReadableStream object.
-  assert(isReadableStreamLike(stream))
+  assert(stream instanceof ReadableStream)
 
   // 6. Let action be null.
   let action = null
@@ -112,7 +110,7 @@ function extractBody (object, keepalive = false) {
 
     // Set source to a copy of the bytes held by object.
     source = new Uint8Array(object.buffer.slice(object.byteOffset, object.byteOffset + object.byteLength))
-  } else if (util.isFormDataLike(object)) {
+  } else if (object instanceof FormData) {
     const boundary = `----formdata-undici-0${`${Math.floor(Math.random() * 1e11)}`.padStart(11, '0')}`
     const prefix = `--${boundary}\r\nContent-Disposition: form-data`
 
@@ -178,7 +176,7 @@ function extractBody (object, keepalive = false) {
     // followed by the multipart/form-data boundary string generated
     // by the multipart/form-data encoding algorithm.
     type = `multipart/form-data; boundary=${boundary}`
-  } else if (isBlobLike(object)) {
+  } else if (object instanceof Blob) {
     // Blob
 
     // Set source to object.
diff --git a/lib/web/fetch/file.js b/lib/web/fetch/file.js
deleted file mode 100644
index 31ba40718ec..00000000000
--- a/lib/web/fetch/file.js
+++ /dev/null
@@ -1,126 +0,0 @@
-'use strict'
-
-const { Blob, File } = require('node:buffer')
-const { kState } = require('./symbols')
-const { webidl } = require('./webidl')
-
-// TODO(@KhafraDev): remove
-class FileLike {
-  constructor (blobLike, fileName, options = {}) {
-    // TODO: argument idl type check
-
-    // The File constructor is invoked with two or three parameters, depending
-    // on whether the optional dictionary parameter is used. When the File()
-    // constructor is invoked, user agents must run the following steps:
-
-    // 1. Let bytes be the result of processing blob parts given fileBits and
-    // options.
-
-    // 2. Let n be the fileName argument to the constructor.
-    const n = fileName
-
-    // 3. Process FilePropertyBag dictionary argument by running the following
-    // substeps:
-
-    //    1. If the type member is provided and is not the empty string, let t
-    //    be set to the type dictionary member. If t contains any characters
-    //    outside the range U+0020 to U+007E, then set t to the empty string
-    //    and return from these substeps.
-    //    TODO
-    const t = options.type
-
-    //    2. Convert every character in t to ASCII lowercase.
-    //    TODO
-
-    //    3. If the lastModified member is provided, let d be set to the
-    //    lastModified dictionary member. If it is not provided, set d to the
-    //    current date and time represented as the number of milliseconds since
-    //    the Unix Epoch (which is the equivalent of Date.now() [ECMA-262]).
-    const d = options.lastModified ?? Date.now()
-
-    // 4. Return a new File object F such that:
-    // F refers to the bytes byte sequence.
-    // F.size is set to the number of total bytes in bytes.
-    // F.name is set to n.
-    // F.type is set to t.
-    // F.lastModified is set to d.
-
-    this[kState] = {
-      blobLike,
-      name: n,
-      type: t,
-      lastModified: d
-    }
-  }
-
-  stream (...args) {
-    webidl.brandCheck(this, FileLike)
-
-    return this[kState].blobLike.stream(...args)
-  }
-
-  arrayBuffer (...args) {
-    webidl.brandCheck(this, FileLike)
-
-    return this[kState].blobLike.arrayBuffer(...args)
-  }
-
-  slice (...args) {
-    webidl.brandCheck(this, FileLike)
-
-    return this[kState].blobLike.slice(...args)
-  }
-
-  text (...args) {
-    webidl.brandCheck(this, FileLike)
-
-    return this[kState].blobLike.text(...args)
-  }
-
-  get size () {
-    webidl.brandCheck(this, FileLike)
-
-    return this[kState].blobLike.size
-  }
-
-  get type () {
-    webidl.brandCheck(this, FileLike)
-
-    return this[kState].blobLike.type
-  }
-
-  get name () {
-    webidl.brandCheck(this, FileLike)
-
-    return this[kState].name
-  }
-
-  get lastModified () {
-    webidl.brandCheck(this, FileLike)
-
-    return this[kState].lastModified
-  }
-
-  get [Symbol.toStringTag] () {
-    return 'File'
-  }
-}
-
-webidl.converters.Blob = webidl.interfaceConverter(Blob)
-
-// If this function is moved to ./util.js, some tools (such as
-// rollup) will warn about circular dependencies. See:
-// https://github.com/nodejs/undici/issues/1629
-function isFileLike (object) {
-  return (
-    (object instanceof File) ||
-    (
-      object &&
-      (typeof object.stream === 'function' ||
-      typeof object.arrayBuffer === 'function') &&
-      object[Symbol.toStringTag] === 'File'
-    )
-  )
-}
-
-module.exports = { FileLike, isFileLike }
diff --git a/lib/web/fetch/formdata-parser.js b/lib/web/fetch/formdata-parser.js
index 7e567e9ec65..90d4d2c7817 100644
--- a/lib/web/fetch/formdata-parser.js
+++ b/lib/web/fetch/formdata-parser.js
@@ -3,7 +3,6 @@
 const { isUSVString, bufferToLowerCasedHeaderName } = require('../../core/util')
 const { utf8DecodeBytes } = require('./util')
 const { HTTP_TOKEN_CODEPOINTS, isomorphicDecode } = require('./data-url')
-const { isFileLike } = require('./file')
 const { makeEntry } = require('./formdata')
 const assert = require('node:assert')
 const { File: NodeFile } = require('node:buffer')
@@ -195,7 +194,7 @@ function multipartFormDataParser (input, mimeType) {
 
     // 5.12. Assert: name is a scalar value string and value is either a scalar value string or a File object.
     assert(isUSVString(name))
-    assert((typeof value === 'string' && isUSVString(value)) || isFileLike(value))
+    assert((typeof value === 'string' && isUSVString(value)) || value instanceof File)
 
     // 5.13. Create an entry with name and value, and append it to entry list.
     entryList.push(makeEntry(name, value, filename))
diff --git a/lib/web/fetch/formdata.js b/lib/web/fetch/formdata.js
index 43e39068d5e..9feea1a0573 100644
--- a/lib/web/fetch/formdata.js
+++ b/lib/web/fetch/formdata.js
@@ -1,9 +1,8 @@
 'use strict'
 
-const { isBlobLike, iteratorMixin } = require('./util')
+const { iteratorMixin } = require('./util')
 const { kState } = require('./symbols')
 const { kEnumerableProperty } = require('../../core/util')
-const { FileLike, isFileLike } = require('./file')
 const { webidl } = require('./webidl')
 const { File: NativeFile } = require('node:buffer')
 const nodeUtil = require('node:util')
@@ -31,7 +30,7 @@ class FormData {
     const prefix = 'FormData.append'
     webidl.argumentLengthCheck(arguments, 2, prefix)
 
-    if (arguments.length === 3 && !isBlobLike(value)) {
+    if (arguments.length === 3 && !(value instanceof Blob)) {
       throw new TypeError(
         "Failed to execute 'append' on 'FormData': parameter 2 is not of type 'Blob'"
       )
@@ -40,8 +39,8 @@ class FormData {
     // 1. Let value be value if given; otherwise blobValue.
 
     name = webidl.converters.USVString(name)
-    value = isBlobLike(value)
-      ? webidl.converters.Blob(value, prefix, 'value', { strict: false })
+    value = value instanceof Blob
+      ? webidl.converters.Blob(value, prefix, 'value')
       : webidl.converters.USVString(value)
     filename = arguments.length === 3
       ? webidl.converters.USVString(filename)
@@ -124,7 +123,7 @@ class FormData {
     const prefix = 'FormData.set'
     webidl.argumentLengthCheck(arguments, 2, prefix)
 
-    if (arguments.length === 3 && !isBlobLike(value)) {
+    if (arguments.length === 3 && !(value instanceof Blob)) {
       throw new TypeError(
         "Failed to execute 'set' on 'FormData': parameter 2 is not of type 'Blob'"
       )
@@ -136,8 +135,8 @@ class FormData {
     // 1. Let value be value if given; otherwise blobValue.
 
     name = webidl.converters.USVString(name)
-    value = isBlobLike(value)
-      ? webidl.converters.Blob(value, prefix, 'name', { strict: false })
+    value = value instanceof Blob
+      ? webidl.converters.Blob(value, prefix, 'name')
       : webidl.converters.USVString(value)
     filename = arguments.length === 3
       ? webidl.converters.USVString(filename)
@@ -222,10 +221,8 @@ function makeEntry (name, value, filename) {
 
     // 1. If value is not a File object, then set value to a new File object,
     //    representing the same bytes, whose name attribute value is "blob"
-    if (!isFileLike(value)) {
-      value = value instanceof Blob
-        ? new File([value], 'blob', { type: value.type })
-        : new FileLike(value, 'blob', { type: value.type })
+    if (!(value instanceof File)) {
+      value = new File([value], 'blob', { type: value.type })
     }
 
     // 2. If filename is given, then set value to a new File object,
@@ -237,9 +234,7 @@ function makeEntry (name, value, filename) {
         lastModified: value.lastModified
       }
 
-      value = value instanceof NativeFile
-        ? new File([value], filename, options)
-        : new FileLike(value, filename, options)
+      value = new File([value], filename, options)
     }
   }
 
diff --git a/lib/web/fetch/index.js b/lib/web/fetch/index.js
index f9b3629c07b..025248d9742 100644
--- a/lib/web/fetch/index.js
+++ b/lib/web/fetch/index.js
@@ -30,7 +30,6 @@ const {
   determineRequestsReferrer,
   coarsenedSharedCurrentTime,
   createDeferredPromise,
-  isBlobLike,
   sameOrigin,
   isCancelled,
   isAborted,
@@ -810,7 +809,7 @@ function schemeFetch (fetchParams) {
 
       // 2. If request’s method is not `GET`, blobURLEntry is null, or blobURLEntry’s
       //    object is not a Blob object, then return a network error.
-      if (request.method !== 'GET' || !isBlobLike(blob)) {
+      if (request.method !== 'GET' || !(blob instanceof Blob)) {
         return Promise.resolve(makeNetworkError('invalid method'))
       }
 
diff --git a/lib/web/fetch/request.js b/lib/web/fetch/request.js
index ca0153922af..b82127f0c6b 100644
--- a/lib/web/fetch/request.js
+++ b/lib/web/fetch/request.js
@@ -400,16 +400,6 @@ class Request {
 
     // 29. If signal is not null, then make this’s signal follow signal.
     if (signal != null) {
-      if (
-        !signal ||
-        typeof signal.aborted !== 'boolean' ||
-        typeof signal.addEventListener !== 'function'
-      ) {
-        throw new TypeError(
-          "Failed to construct 'Request': member signal is not of type AbortSignal."
-        )
-      }
-
       if (signal.aborted) {
         ac.abort(signal.reason)
       } else {
@@ -1011,8 +1001,7 @@ webidl.converters.RequestInit = webidl.dictionaryConverter([
       (signal) => webidl.converters.AbortSignal(
         signal,
         'RequestInit',
-        'signal',
-        { strict: false }
+        'signal'
       )
     )
   },
diff --git a/lib/web/fetch/response.js b/lib/web/fetch/response.js
index 155dbadd1ad..252addc2286 100644
--- a/lib/web/fetch/response.js
+++ b/lib/web/fetch/response.js
@@ -9,7 +9,6 @@ const {
   isValidReasonPhrase,
   isCancelled,
   isAborted,
-  isBlobLike,
   serializeJavascriptValueToJSONString,
   isErrorLike,
   isomorphicEncode,
@@ -541,16 +540,16 @@ webidl.converters.XMLHttpRequestBodyInit = function (V, prefix, name) {
     return webidl.converters.USVString(V, prefix, name)
   }
 
-  if (isBlobLike(V)) {
-    return webidl.converters.Blob(V, prefix, name, { strict: false })
+  if (V instanceof Blob) {
+    return webidl.converters.Blob(V, prefix, name)
   }
 
   if (ArrayBuffer.isView(V) || types.isArrayBuffer(V)) {
     return webidl.converters.BufferSource(V, prefix, name)
   }
 
-  if (util.isFormDataLike(V)) {
-    return webidl.converters.FormData(V, prefix, name, { strict: false })
+  if (V instanceof FormData) {
+    return webidl.converters.FormData(V, prefix, name)
   }
 
   if (V instanceof URLSearchParams) {
diff --git a/lib/web/fetch/util.js b/lib/web/fetch/util.js
index 623b475854f..28d54fe946c 100644
--- a/lib/web/fetch/util.js
+++ b/lib/web/fetch/util.js
@@ -6,7 +6,7 @@ const { redirectStatusSet, referrerPolicySet: referrerPolicyTokens, badPortsSet
 const { getGlobalOrigin } = require('./global')
 const { collectASequenceOfCodePoints, collectAnHTTPQuotedString, removeChars, parseMIMEType } = require('./data-url')
 const { performance } = require('node:perf_hooks')
-const { isBlobLike, ReadableStreamFrom, isValidHTTPToken, normalizedMethodRecordsBase } = require('../../core/util')
+const { ReadableStreamFrom, isValidHTTPToken, normalizedMethodRecordsBase } = require('../../core/util')
 const assert = require('node:assert')
 const { isUint8Array } = require('node:util/types')
 const { webidl } = require('./webidl')
@@ -1061,13 +1061,6 @@ async function fullyReadBody (body, processBody, processBodyError) {
   }
 }
 
-function isReadableStreamLike (stream) {
-  return stream instanceof ReadableStream || (
-    stream[Symbol.toStringTag] === 'ReadableStream' &&
-    typeof stream.tee === 'function'
-  )
-}
-
 /**
  * @param {ReadableStreamController<Uint8Array>} controller
  */
@@ -1589,7 +1582,6 @@ module.exports = {
   requestCurrentURL,
   responseURL,
   responseLocationURL,
-  isBlobLike,
   isURLPotentiallyTrustworthy,
   isValidReasonPhrase,
   sameOrigin,
@@ -1602,7 +1594,6 @@ module.exports = {
   isErrorLike,
   fullyReadBody,
   bytesMatch,
-  isReadableStreamLike,
   readableStreamClose,
   isomorphicEncode,
   urlIsLocal,
diff --git a/lib/web/fetch/webidl.js b/lib/web/fetch/webidl.js
index de185fdea3a..ef0e6dc27f1 100644
--- a/lib/web/fetch/webidl.js
+++ b/lib/web/fetch/webidl.js
@@ -33,14 +33,8 @@ webidl.errors.invalidArgument = function (context) {
 }
 
 // https://webidl.spec.whatwg.org/#implements
-webidl.brandCheck = function (V, I, opts) {
-  if (opts?.strict !== false && !(V instanceof I)) {
-    const err = new TypeError('Illegal invocation')
-    err.code = 'ERR_INVALID_THIS' // node compat.
-    throw err
-  } else if (V?.[Symbol.toStringTag] !== I.prototype[Symbol.toStringTag]) {
-    // TODO(@KhafraDev): this check does not work properly on extended classes
-
+webidl.brandCheck = function (V, I) {
+  if (!(V instanceof I)) {
     const err = new TypeError('Illegal invocation')
     err.code = 'ERR_INVALID_THIS' // node compat.
     throw err
@@ -346,8 +340,8 @@ webidl.recordConverter = function (keyConverter, valueConverter) {
 }
 
 webidl.interfaceConverter = function (i) {
-  return (V, prefix, argument, opts) => {
-    if (opts?.strict !== false && !(V instanceof i)) {
+  return (V, prefix, argument) => {
+    if (!(V instanceof i)) {
       throw webidl.errors.exception({
         header: prefix,
         message: `Expected ${argument} ("${webidl.util.Stringify(V)}") to be an instance of ${i.name}.`
@@ -694,6 +688,8 @@ webidl.converters['record<ByteString, ByteString>'] = webidl.recordConverter(
   webidl.converters.ByteString
 )
 
+webidl.converters.Blob = webidl.interfaceConverter(Blob)
+
 module.exports = {
   webidl
 }
diff --git a/lib/web/websocket/websocket.js b/lib/web/websocket/websocket.js
index 345f2888cc4..96d6c4e453d 100644
--- a/lib/web/websocket/websocket.js
+++ b/lib/web/websocket/websocket.js
@@ -17,7 +17,7 @@ const {
 } = require('./util')
 const { establishWebSocketConnection, closeWebSocketConnection } = require('./connection')
 const { ByteParser } = require('./receiver')
-const { kEnumerableProperty, isBlobLike } = require('../../core/util')
+const { kEnumerableProperty } = require('../../core/util')
 const { getGlobalDispatcher } = require('../../global')
 const { types } = require('node:util')
 const { ErrorEvent, CloseEvent, createFastMessageEvent } = require('./events')
@@ -324,7 +324,7 @@ class WebSocket extends EventTarget {
       this.#sendQueue.add(data, () => {
         this.#bufferedAmount -= data.byteLength
       }, sendHints.typedArray)
-    } else if (isBlobLike(data)) {
+    } else if (data instanceof Blob) {
       // If the WebSocket connection is established, and the WebSocket
       // closing handshake has not yet started, then the user agent must
       // send a WebSocket Message comprised of data using a binary frame
@@ -793,8 +793,8 @@ webidl.converters['DOMString or sequence<DOMString> or WebSocketInit'] = functio
 
 webidl.converters.WebSocketSendData = function (V) {
   if (webidl.util.Type(V) === 'Object') {
-    if (isBlobLike(V)) {
-      return webidl.converters.Blob(V, { strict: false })
+    if (V instanceof Blob) {
+      return webidl.converters.Blob(V)
     }
 
     if (ArrayBuffer.isView(V) || types.isArrayBuffer(V)) {
diff --git a/package.json b/package.json
index 7319b3e9eec..5737e0c74eb 100644
--- a/package.json
+++ b/package.json
@@ -113,12 +113,9 @@
     "dns-packet": "^5.4.0",
     "eslint": "^9.9.0",
     "fast-check": "^3.17.1",
-    "form-data": "^4.0.0",
-    "formdata-node": "^6.0.3",
     "https-pem": "^3.0.0",
     "husky": "^9.0.7",
     "jest": "^29.0.2",
-    "jsdom": "^25.0.0",
     "neostandard": "^0.11.2",
     "node-forge": "^1.3.1",
     "pre-commit": "^1.2.2",
diff --git a/test/fetch/abort.js b/test/fetch/abort.js
index 018c9a10b68..73b4764fe81 100644
--- a/test/fetch/abort.js
+++ b/test/fetch/abort.js
@@ -6,39 +6,8 @@ const { tspl } = require('@matteo.collina/tspl')
 const { fetch } = require('../..')
 const { createServer } = require('node:http')
 const { once } = require('node:events')
-
 const { closeServerAsPromise } = require('../utils/node-http')
 
-const { AbortController: NPMAbortController } = require('abort-controller')
-
-test('Allow the usage of custom implementation of AbortController', async (t) => {
-  const body = {
-    fixes: 1605
-  }
-
-  const server = createServer((req, res) => {
-    res.statusCode = 200
-    res.end(JSON.stringify(body))
-  })
-
-  t.after(closeServerAsPromise(server))
-
-  server.listen(0)
-  await once(server, 'listening')
-
-  const controller = new NPMAbortController()
-  const signal = controller.signal
-  controller.abort()
-
-  try {
-    await fetch(`http://localhost:${server.address().port}`, {
-      signal
-    })
-  } catch (e) {
-    assert.strictEqual(e.code, DOMException.ABORT_ERR)
-  }
-})
-
 test('allows aborting with custom errors', async (t) => {
   const server = createServer().listen(0)
 
diff --git a/test/fetch/formdata.js b/test/fetch/formdata.js
index 31b563b0763..997e77ebabf 100644
--- a/test/fetch/formdata.js
+++ b/test/fetch/formdata.js
@@ -4,10 +4,8 @@ const { test } = require('node:test')
 const assert = require('node:assert')
 const { tspl } = require('@matteo.collina/tspl')
 const { FormData, Response, Request } = require('../../')
-const { Blob: ThirdPartyBlob } = require('formdata-node')
 const { Blob, File } = require('node:buffer')
 const { isFormDataLike } = require('../../lib/core/util')
-const ThirdPartyFormDataInvalid = require('form-data')
 
 test('arg validation', () => {
   const form = new FormData()
@@ -110,17 +108,6 @@ test('append blob', async () => {
   assert.strictEqual(form.get('asd'), null)
 })
 
-test('append third-party blob', async () => {
-  const form = new FormData()
-  form.set('asd', new ThirdPartyBlob(['asd1'], { type: 'text/plain' }))
-
-  assert.strictEqual(form.has('asd'), true)
-  assert.strictEqual(form.get('asd').type, 'text/plain')
-  assert.strictEqual(await form.get('asd').text(), 'asd1')
-  form.delete('asd')
-  assert.strictEqual(form.get('asd'), null)
-})
-
 test('append string', () => {
   const form = new FormData()
   form.set('k1', 'v1')
@@ -304,11 +291,6 @@ test('formData should be an instance of FormData', async (t) => {
     assert.strictEqual(isFormDataLike(form), false)
   })
 
-  await t.test('Invalid third-party FormData', () => {
-    const form = new ThirdPartyFormDataInvalid()
-    assert.strictEqual(isFormDataLike(form), false)
-  })
-
   await t.test('Valid FormData', () => {
     const form = new FormData()
     assert.strictEqual(isFormDataLike(form), true)
diff --git a/test/fetch/jsdom-abortcontroller-1910-1464495619.js b/test/fetch/jsdom-abortcontroller-1910-1464495619.js
deleted file mode 100644
index b59ef9f95ca..00000000000
--- a/test/fetch/jsdom-abortcontroller-1910-1464495619.js
+++ /dev/null
@@ -1,27 +0,0 @@
-'use strict'
-
-const { test } = require('node:test')
-const assert = require('node:assert')
-const { createServer } = require('node:http')
-const { once } = require('node:events')
-const { fetch } = require('../..')
-const { JSDOM } = require('jsdom')
-
-// https://github.com/nodejs/undici/pull/1910#issuecomment-1464495619
-test('third party AbortControllers', async (t) => {
-  const server = createServer((_, res) => res.end()).listen(0)
-
-  const { AbortController } = new JSDOM().window
-  let controller = new AbortController()
-
-  t.after(() => {
-    controller.abort()
-    controller = null
-    return server.close()
-  })
-  await once(server, 'listening')
-
-  await assert.doesNotReject(fetch(`http://localhost:${server.address().port}`, {
-    signal: controller.signal
-  }))
-})
diff --git a/test/fetch/request.js b/test/fetch/request.js
index 2cc1f6437de..64ead02f0ff 100644
--- a/test/fetch/request.js
+++ b/test/fetch/request.js
@@ -11,10 +11,6 @@ const {
   fetch
 } = require('../../')
 const { fromInnerRequest, makeRequest } = require('../../lib/web/fetch/request')
-const {
-  Blob: ThirdPartyBlob,
-  FormData: ThirdPartyFormData
-} = require('formdata-node')
 const { kState, kSignal, kHeaders } = require('../../lib/web/fetch/symbols')
 const { getHeadersGuard, getHeadersList } = require('../../lib/web/fetch/headers')
 
@@ -419,26 +415,6 @@ test('RequestInit.signal option', async () => {
   }), TypeError)
 })
 
-test('constructing Request with third party Blob body', async () => {
-  const blob = new ThirdPartyBlob(['text'])
-  const req = new Request('http://asd', {
-    method: 'POST',
-    body: blob
-  })
-  assert.strictEqual(await req.text(), 'text')
-})
-test('constructing Request with third party FormData body', async () => {
-  const form = new ThirdPartyFormData()
-  form.set('key', 'value')
-  const req = new Request('http://asd', {
-    method: 'POST',
-    body: form
-  })
-  const contentType = req.headers.get('content-type').split('=')
-  assert.strictEqual(contentType[0], 'multipart/form-data; boundary')
-  assert.ok((await req.text()).startsWith(`--${contentType[1]}`))
-})
-
 // https://github.com/nodejs/undici/issues/2050
 test('set-cookie headers get cleared when passing a Request as first param', () => {
   const req1 = new Request('http://localhost', {
diff --git a/test/fetch/response.js b/test/fetch/response.js
index 8e7c865c78e..58c04a27422 100644
--- a/test/fetch/response.js
+++ b/test/fetch/response.js
@@ -10,10 +10,6 @@ const {
   FormData
 } = require('../../')
 const { fromInnerResponse, makeResponse } = require('../../lib/web/fetch/response')
-const {
-  Blob: ThirdPartyBlob,
-  FormData: ThirdPartyFormData
-} = require('formdata-node')
 const { kState, kHeaders } = require('../../lib/web/fetch/symbols')
 const { getHeadersGuard, getHeadersList } = require('../../lib/web/fetch/headers')
 
@@ -239,20 +235,6 @@ test('constructing a Response with a ReadableStream body', async (t) => {
   })
 })
 
-test('constructing Response with third party Blob body', async () => {
-  const blob = new ThirdPartyBlob(['text'])
-  const res = new Response(blob)
-  assert.strictEqual(await res.text(), 'text')
-})
-test('constructing Response with third party FormData body', async () => {
-  const form = new ThirdPartyFormData()
-  form.set('key', 'value')
-  const res = new Response(form)
-  const contentType = res.headers.get('content-type').split('=')
-  assert.strictEqual(contentType[0], 'multipart/form-data; boundary')
-  assert.ok((await res.text()).startsWith(`--${contentType[1]}`))
-})
-
 // https://github.com/nodejs/undici/issues/2465
 test('Issue#2465', async (t) => {
   const { strictEqual } = tspl(t, { plan: 1 })
diff --git a/test/issue-2065.js b/test/issue-2065.js
index b84fe04085b..9037fb557c3 100644
--- a/test/issue-2065.js
+++ b/test/issue-2065.js
@@ -4,7 +4,6 @@ const { tspl } = require('@matteo.collina/tspl')
 const { test, after } = require('node:test')
 const { createServer } = require('node:http')
 const { once } = require('node:events')
-const { createReadStream } = require('node:fs')
 const { FormData, request } = require('..')
 const { File } = require('node:buffer')
 
@@ -27,45 +26,3 @@ test('undici.request with a FormData body should set content-length header', asy
     body
   })
 })
-
-test('undici.request with a FormData stream value should set transfer-encoding header', async (t) => {
-  t = tspl(t, { plan: 1 })
-
-  const server = createServer((req, res) => {
-    t.strictEqual(req.headers['transfer-encoding'], 'chunked')
-    res.end()
-  }).listen(0)
-
-  after(() => server.close())
-  await once(server, 'listening')
-
-  class BlobFromStream {
-    #stream
-    #type
-    constructor (stream, type) {
-      this.#stream = stream
-      this.#type = type
-    }
-
-    stream () {
-      return this.#stream
-    }
-
-    get type () {
-      return this.#type
-    }
-
-    get [Symbol.toStringTag] () {
-      return 'Blob'
-    }
-  }
-
-  const body = new FormData()
-  const fileReadable = createReadStream(__filename)
-  body.set('file', new BlobFromStream(fileReadable, '.js'), 'streamfile')
-
-  await request(`http://localhost:${server.address().port}`, {
-    method: 'POST',
-    body
-  })
-})
diff --git a/test/node-fetch/main.js b/test/node-fetch/main.js
index 2360620740c..6d2e73b455d 100644
--- a/test/node-fetch/main.js
+++ b/test/node-fetch/main.js
@@ -919,9 +919,9 @@ describe('node-fetch', () => {
 
   it('should throw a TypeError if a signal is not of type AbortSignal or EventTarget', () => {
     return Promise.all([
-      assert.rejects(fetch(`${base}inspect`, { signal: {} }), new TypeError("Failed to construct 'Request': member signal is not of type AbortSignal.")),
-      assert.rejects(fetch(`${base}inspect`, { signal: '' }), new TypeError("Failed to construct 'Request': member signal is not of type AbortSignal.")),
-      assert.rejects(fetch(`${base}inspect`, { signal: Object.create(null) }), new TypeError("Failed to construct 'Request': member signal is not of type AbortSignal."))
+      assert.rejects(fetch(`${base}inspect`, { signal: {} }), new TypeError('RequestInit: Expected signal ("{}") to be an instance of AbortSignal.')),
+      assert.rejects(fetch(`${base}inspect`, { signal: '' }), new TypeError('RequestInit: Expected signal ("""") to be an instance of AbortSignal.')),
+      assert.rejects(fetch(`${base}inspect`, { signal: Object.create(null) }), new TypeError('RequestInit: Expected signal ("[Object: null prototype] {}") to be an instance of AbortSignal.'))
     ])
   })
 
diff --git a/types/webidl.d.ts b/types/webidl.d.ts
index 7ea596cafd0..eebe99c801c 100644
--- a/types/webidl.d.ts
+++ b/types/webidl.d.ts
@@ -167,7 +167,7 @@ export interface Webidl {
    * @description Performs a brand-check on {@param V} to ensure it is a
    * {@param cls} object.
    */
-  brandCheck <Interface extends new () => unknown>(V: unknown, cls: Interface, opts?: { strict?: boolean }): asserts V is Interface
+  brandCheck <Interface extends new () => unknown>(V: unknown, cls: Interface): asserts V is Interface
 
   brandCheckMultiple <Interfaces extends (new () => unknown)[]> (V: unknown, list: Interfaces): asserts V is Interfaces[number]
 
@@ -194,7 +194,8 @@ export interface Webidl {
    */
   interfaceConverter <Interface>(cls: Interface): (
     V: unknown,
-    opts?: { strict: boolean }
+    prefix: string,
+    argument: string
   ) => asserts V is typeof cls
 
   // TODO(@KhafraDev): a type could likely be implemented that can infer the return type