diff --git a/lib/fetch/body.js b/lib/fetch/body.js
index beb1e027c98..0761302c9b9 100644
--- a/lib/fetch/body.js
+++ b/lib/fetch/body.js
@@ -262,100 +262,132 @@ function cloneBody (body) {
   }
 }
 
-const methods = {
-  async blob () {
-    const chunks = []
+function bodyMixinMethods (instance) {
+  const methods = {
+    async blob () {
+      if (!(this instanceof instance)) {
+        throw new TypeError('Illegal invocation')
+      }
 
-    if (this[kState].body) {
-      if (isUint8Array(this[kState].body)) {
-        chunks.push(this[kState].body)
-      } else {
-        const stream = this[kState].body.stream
+      const chunks = []
 
-        if (util.isDisturbed(stream)) {
-          throw new TypeError('disturbed')
-        }
+      if (this[kState].body) {
+        if (isUint8Array(this[kState].body)) {
+          chunks.push(this[kState].body)
+        } else {
+          const stream = this[kState].body.stream
 
-        if (stream.locked) {
-          throw new TypeError('locked')
-        }
+          if (util.isDisturbed(stream)) {
+            throw new TypeError('disturbed')
+          }
+
+          if (stream.locked) {
+            throw new TypeError('locked')
+          }
 
-        // Compat.
-        stream[kBodyUsed] = true
+          // Compat.
+          stream[kBodyUsed] = true
 
-        for await (const chunk of stream) {
-          chunks.push(chunk)
+          for await (const chunk of stream) {
+            chunks.push(chunk)
+          }
         }
       }
-    }
 
-    return new Blob(chunks, { type: this.headers.get('Content-Type') || '' })
-  },
+      return new Blob(chunks, { type: this.headers.get('Content-Type') || '' })
+    },
 
-  async arrayBuffer () {
-    const blob = await this.blob()
-    return await blob.arrayBuffer()
-  },
+    async arrayBuffer () {
+      if (!(this instanceof instance)) {
+        throw new TypeError('Illegal invocation')
+      }
 
-  async text () {
-    const blob = await this.blob()
-    return toUSVString(await blob.text())
-  },
+      const blob = await this.blob()
+      return await blob.arrayBuffer()
+    },
 
-  async json () {
-    return JSON.parse(await this.text())
-  },
+    async text () {
+      if (!(this instanceof instance)) {
+        throw new TypeError('Illegal invocation')
+      }
+
+      const blob = await this.blob()
+      return toUSVString(await blob.text())
+    },
 
-  async formData () {
-    const contentType = this.headers.get('Content-Type')
-
-    // If mimeType’s essence is "multipart/form-data", then:
-    if (/multipart\/form-data/.test(contentType)) {
-      throw new NotSupportedError('multipart/form-data not supported')
-    } else if (/application\/x-www-form-urlencoded/.test(contentType)) {
-      // Otherwise, if mimeType’s essence is "application/x-www-form-urlencoded", then:
-
-      // 1. Let entries be the result of parsing bytes.
-      let entries
-      try {
-        entries = new URLSearchParams(await this.text())
-      } catch (err) {
-        // istanbul ignore next: Unclear when new URLSearchParams can fail on a string.
-        // 2. If entries is failure, then throw a TypeError.
-        throw Object.assign(new TypeError(), { cause: err })
+    async json () {
+      if (!(this instanceof instance)) {
+        throw new TypeError('Illegal invocation')
       }
 
-      // 3. Return a new FormData object whose entries are entries.
-      const formData = new FormData()
-      for (const [name, value] of entries) {
-        formData.append(name, value)
+      return JSON.parse(await this.text())
+    },
+
+    async formData () {
+      if (!(this instanceof instance)) {
+        throw new TypeError('Illegal invocation')
+      }
+
+      const contentType = this.headers.get('Content-Type')
+
+      // If mimeType’s essence is "multipart/form-data", then:
+      if (/multipart\/form-data/.test(contentType)) {
+        throw new NotSupportedError('multipart/form-data not supported')
+      } else if (/application\/x-www-form-urlencoded/.test(contentType)) {
+        // Otherwise, if mimeType’s essence is "application/x-www-form-urlencoded", then:
+
+        // 1. Let entries be the result of parsing bytes.
+        let entries
+        try {
+          entries = new URLSearchParams(await this.text())
+        } catch (err) {
+          // istanbul ignore next: Unclear when new URLSearchParams can fail on a string.
+          // 2. If entries is failure, then throw a TypeError.
+          throw Object.assign(new TypeError(), { cause: err })
+        }
+
+        // 3. Return a new FormData object whose entries are entries.
+        const formData = new FormData()
+        for (const [name, value] of entries) {
+          formData.append(name, value)
+        }
+        return formData
+      } else {
+        // Otherwise, throw a TypeError.
+        throw new TypeError()
       }
-      return formData
-    } else {
-      // Otherwise, throw a TypeError.
-      throw new TypeError()
     }
   }
+
+  return methods
 }
 
 const properties = {
   body: {
     enumerable: true,
     get () {
+      if (!this || !this[kState]) {
+        throw new TypeError('Illegal invocation')
+      }
+
       return this[kState].body ? this[kState].body.stream : null
     }
   },
   bodyUsed: {
     enumerable: true,
     get () {
+      if (!this || !this[kState]) {
+        throw new TypeError('Illegal invocation')
+      }
+
       return !!this[kState].body && util.isDisturbed(this[kState].body.stream)
     }
   }
 }
 
 function mixinBody (prototype) {
-  Object.assign(prototype, methods)
-  Object.defineProperties(prototype, properties)
+  Object.assign(prototype.prototype, bodyMixinMethods(prototype))
+  Object.defineProperties(prototype.prototype, properties)
 }
 
 module.exports = {
diff --git a/lib/fetch/request.js b/lib/fetch/request.js
index 42c7eb447a2..e0a82bf095e 100644
--- a/lib/fetch/request.js
+++ b/lib/fetch/request.js
@@ -748,7 +748,7 @@ class Request {
   }
 }
 
-mixinBody(Request.prototype)
+mixinBody(Request)
 
 function makeRequest (init) {
   // https://fetch.spec.whatwg.org/#requests
diff --git a/lib/fetch/response.js b/lib/fetch/response.js
index 582876e050a..68c5c01e51e 100644
--- a/lib/fetch/response.js
+++ b/lib/fetch/response.js
@@ -287,7 +287,7 @@ class Response {
     return clonedResponseObject
   }
 }
-mixinBody(Response.prototype)
+mixinBody(Response)
 
 Object.defineProperties(Response.prototype, {
   type: kEnumerableProperty,
diff --git a/test/fetch/request.js b/test/fetch/request.js
index fbc8f075fc2..375107089d7 100644
--- a/test/fetch/request.js
+++ b/test/fetch/request.js
@@ -9,7 +9,7 @@ const {
 } = require('../../')
 const { kState } = require('../../lib/fetch/symbols.js')
 
-test('arg validation', (t) => {
+test('arg validation', async (t) => {
   // constructor
   t.throws(() => {
     // eslint-disable-next-line
@@ -144,6 +144,16 @@ test('arg validation', (t) => {
     Request.prototype.signal.toString()
   }, TypeError)
 
+  t.throws(() => {
+    // eslint-disable-next-line no-unused-expressions
+    Request.prototype.body
+  }, TypeError)
+
+  t.throws(() => {
+    // eslint-disable-next-line no-unused-expressions
+    Request.prototype.bodyUsed
+  }, TypeError)
+
   t.throws(() => {
     Request.prototype.clone.call(null)
   }, TypeError)
@@ -152,6 +162,26 @@ test('arg validation', (t) => {
     Request.prototype[Symbol.toStringTag].charAt(0)
   })
 
+  for (const method of [
+    'text',
+    'json',
+    'arrayBuffer',
+    'blob',
+    'formData'
+  ]) {
+    await t.rejects(async () => {
+      await new Request('http://localhost')[method].call({
+        blob () {
+          return {
+            text () {
+              return Promise.resolve('emulating this')
+            }
+          }
+        }
+      })
+    }, TypeError)
+  }
+
   t.end()
 })
 
diff --git a/test/fetch/response.js b/test/fetch/response.js
index 374c84034e9..f1e12467620 100644
--- a/test/fetch/response.js
+++ b/test/fetch/response.js
@@ -5,7 +5,7 @@ const {
   Response
 } = require('../../')
 
-test('arg validation', (t) => {
+test('arg validation', async (t) => {
   // constructor
   t.throws(() => {
     // eslint-disable-next-line
@@ -77,10 +77,32 @@ test('arg validation', (t) => {
     Response.prototype.headers.toString()
   }, TypeError)
 
+  t.throws(() => {
+    // eslint-disable-next-line no-unused-expressions
+    Response.prototype.body
+  }, TypeError)
+
+  t.throws(() => {
+    // eslint-disable-next-line no-unused-expressions
+    Response.prototype.bodyUsed
+  }, TypeError)
+
   t.throws(() => {
     Response.prototype.clone.call(null)
   }, TypeError)
 
+  await t.rejects(async () => {
+    await new Response('http://localhost').text.call({
+      blob () {
+        return {
+          text () {
+            return Promise.resolve('emulating response.blob()')
+          }
+        }
+      }
+    })
+  }, TypeError)
+
   t.end()
 })