diff --git a/lib/internal/webstreams/encoding.js b/lib/internal/webstreams/encoding.js
index b95441e12e0cf1..b5533b4287b65a 100644
--- a/lib/internal/webstreams/encoding.js
+++ b/lib/internal/webstreams/encoding.js
@@ -4,7 +4,6 @@ const {
   ObjectDefineProperties,
   String,
   StringPrototypeCharCodeAt,
-  Symbol,
   Uint8Array,
 } = primordials;
 
@@ -31,32 +30,19 @@ const {
   kEnumerableProperty,
 } = require('internal/util');
 
-const kHandle = Symbol('kHandle');
-const kTransform = Symbol('kTransform');
-const kType = Symbol('kType');
-const kPendingHighSurrogate = Symbol('kPendingHighSurrogate');
-
 /**
  * @typedef {import('./readablestream').ReadableStream} ReadableStream
  * @typedef {import('./writablestream').WritableStream} WritableStream
  */
 
-function isTextEncoderStream(value) {
-  return typeof value?.[kHandle] === 'object' &&
-         value?.[kType] === 'TextEncoderStream';
-}
-
-function isTextDecoderStream(value) {
-  return typeof value?.[kHandle] === 'object' &&
-         value?.[kType] === 'TextDecoderStream';
-}
-
 class TextEncoderStream {
+  #pendingHighSurrogate = null;
+  #handle;
+  #transform;
+
   constructor() {
-    this[kPendingHighSurrogate] = null;
-    this[kType] = 'TextEncoderStream';
-    this[kHandle] = new TextEncoder();
-    this[kTransform] = new TransformStream({
+    this.#handle = new TextEncoder();
+    this.#transform = new TransformStream({
       transform: (chunk, controller) => {
         // https://encoding.spec.whatwg.org/#encode-and-enqueue-a-chunk
         chunk = String(chunk);
@@ -64,9 +50,9 @@ class TextEncoderStream {
         for (let i = 0; i < chunk.length; i++) {
           const item = chunk[i];
           const codeUnit = StringPrototypeCharCodeAt(item, 0);
-          if (this[kPendingHighSurrogate] !== null) {
-            const highSurrogate = this[kPendingHighSurrogate];
-            this[kPendingHighSurrogate] = null;
+          if (this.#pendingHighSurrogate !== null) {
+            const highSurrogate = this.#pendingHighSurrogate;
+            this.#pendingHighSurrogate = null;
             if (0xDC00 <= codeUnit && codeUnit <= 0xDFFF) {
               finalChunk += highSurrogate + item;
               continue;
@@ -74,7 +60,7 @@ class TextEncoderStream {
             finalChunk += '\uFFFD';
           }
           if (0xD800 <= codeUnit && codeUnit <= 0xDBFF) {
-            this[kPendingHighSurrogate] = item;
+            this.#pendingHighSurrogate = item;
             continue;
           }
           if (0xDC00 <= codeUnit && codeUnit <= 0xDFFF) {
@@ -84,13 +70,13 @@ class TextEncoderStream {
           finalChunk += item;
         }
         if (finalChunk) {
-          const value = this[kHandle].encode(finalChunk);
+          const value = this.#handle.encode(finalChunk);
           controller.enqueue(value);
         }
       },
       flush: (controller) => {
         // https://encoding.spec.whatwg.org/#encode-and-flush
-        if (this[kPendingHighSurrogate] !== null) {
+        if (this.#pendingHighSurrogate !== null) {
           controller.enqueue(new Uint8Array([0xEF, 0xBF, 0xBD]));
         }
       },
@@ -102,9 +88,7 @@ class TextEncoderStream {
    * @type {string}
    */
   get encoding() {
-    if (!isTextEncoderStream(this))
-      throw new ERR_INVALID_THIS('TextEncoderStream');
-    return this[kHandle].encoding;
+    return this.#handle.encoding;
   }
 
   /**
@@ -112,9 +96,7 @@ class TextEncoderStream {
    * @type {ReadableStream}
    */
   get readable() {
-    if (!isTextEncoderStream(this))
-      throw new ERR_INVALID_THIS('TextEncoderStream');
-    return this[kTransform].readable;
+    return this.#transform.readable;
   }
 
   /**
@@ -122,23 +104,24 @@ class TextEncoderStream {
    * @type {WritableStream}
    */
   get writable() {
-    if (!isTextEncoderStream(this))
-      throw new ERR_INVALID_THIS('TextEncoderStream');
-    return this[kTransform].writable;
+    return this.#transform.writable;
   }
 
   [kInspect](depth, options) {
-    if (!isTextEncoderStream(this))
+    if (this == null)
       throw new ERR_INVALID_THIS('TextEncoderStream');
     return customInspect(depth, options, 'TextEncoderStream', {
-      encoding: this[kHandle].encoding,
-      readable: this[kTransform].readable,
-      writable: this[kTransform].writable,
+      encoding: this.#handle.encoding,
+      readable: this.#transform.readable,
+      writable: this.#transform.writable,
     });
   }
 }
 
 class TextDecoderStream {
+  #handle;
+  #transform;
+
   /**
    * @param {string} [encoding]
    * @param {{
@@ -147,16 +130,15 @@ class TextDecoderStream {
    * }} [options]
    */
   constructor(encoding = 'utf-8', options = kEmptyObject) {
-    this[kType] = 'TextDecoderStream';
-    this[kHandle] = new TextDecoder(encoding, options);
-    this[kTransform] = new TransformStream({
+    this.#handle = new TextDecoder(encoding, options);
+    this.#transform = new TransformStream({
       transform: (chunk, controller) => {
-        const value = this[kHandle].decode(chunk, { stream: true });
+        const value = this.#handle.decode(chunk, { stream: true });
         if (value)
           controller.enqueue(value);
       },
       flush: (controller) => {
-        const value = this[kHandle].decode();
+        const value = this.#handle.decode();
         if (value)
           controller.enqueue(value);
         controller.terminate();
@@ -169,9 +151,7 @@ class TextDecoderStream {
    * @type {string}
    */
   get encoding() {
-    if (!isTextDecoderStream(this))
-      throw new ERR_INVALID_THIS('TextDecoderStream');
-    return this[kHandle].encoding;
+    return this.#handle.encoding;
   }
 
   /**
@@ -179,9 +159,7 @@ class TextDecoderStream {
    * @type {boolean}
    */
   get fatal() {
-    if (!isTextDecoderStream(this))
-      throw new ERR_INVALID_THIS('TextDecoderStream');
-    return this[kHandle].fatal;
+    return this.#handle.fatal;
   }
 
   /**
@@ -189,9 +167,7 @@ class TextDecoderStream {
    * @type {boolean}
    */
   get ignoreBOM() {
-    if (!isTextDecoderStream(this))
-      throw new ERR_INVALID_THIS('TextDecoderStream');
-    return this[kHandle].ignoreBOM;
+    return this.#handle.ignoreBOM;
   }
 
   /**
@@ -199,9 +175,7 @@ class TextDecoderStream {
    * @type {ReadableStream}
    */
   get readable() {
-    if (!isTextDecoderStream(this))
-      throw new ERR_INVALID_THIS('TextDecoderStream');
-    return this[kTransform].readable;
+    return this.#transform.readable;
   }
 
   /**
@@ -209,20 +183,18 @@ class TextDecoderStream {
    * @type {WritableStream}
    */
   get writable() {
-    if (!isTextDecoderStream(this))
-      throw new ERR_INVALID_THIS('TextDecoderStream');
-    return this[kTransform].writable;
+    return this.#transform.writable;
   }
 
   [kInspect](depth, options) {
-    if (!isTextDecoderStream(this))
+    if (this == null)
       throw new ERR_INVALID_THIS('TextDecoderStream');
     return customInspect(depth, options, 'TextDecoderStream', {
-      encoding: this[kHandle].encoding,
-      fatal: this[kHandle].fatal,
-      ignoreBOM: this[kHandle].ignoreBOM,
-      readable: this[kTransform].readable,
-      writable: this[kTransform].writable,
+      encoding: this.#handle.encoding,
+      fatal: this.#handle.fatal,
+      ignoreBOM: this.#handle.ignoreBOM,
+      readable: this.#transform.readable,
+      writable: this.#transform.writable,
     });
   }
 }
diff --git a/test/parallel/test-whatwg-webstreams-encoding.js b/test/parallel/test-whatwg-webstreams-encoding.js
index 97061650496c0d..b2b18df73bf1fe 100644
--- a/test/parallel/test-whatwg-webstreams-encoding.js
+++ b/test/parallel/test-whatwg-webstreams-encoding.js
@@ -48,23 +48,28 @@ const kEuro = Buffer.from([0xe2, 0x82, 0xac]).toString();
 
   assert.throws(
     () => Reflect.get(TextDecoderStream.prototype, 'encoding', {}), {
-      code: 'ERR_INVALID_THIS',
+      name: 'TypeError',
+      message: /Cannot read private member/,
     });
   assert.throws(
     () => Reflect.get(TextDecoderStream.prototype, 'fatal', {}), {
-      code: 'ERR_INVALID_THIS',
+      name: 'TypeError',
+      message: /Cannot read private member/,
     });
   assert.throws(
     () => Reflect.get(TextDecoderStream.prototype, 'ignoreBOM', {}), {
-      code: 'ERR_INVALID_THIS',
+      name: 'TypeError',
+      message: /Cannot read private member/,
     });
   assert.throws(
     () => Reflect.get(TextDecoderStream.prototype, 'readable', {}), {
-      code: 'ERR_INVALID_THIS',
+      name: 'TypeError',
+      message: /Cannot read private member/,
     });
   assert.throws(
     () => Reflect.get(TextDecoderStream.prototype, 'writable', {}), {
-      code: 'ERR_INVALID_THIS',
+      name: 'TypeError',
+      message: /Cannot read private member/,
     });
 }
 
@@ -89,14 +94,17 @@ const kEuro = Buffer.from([0xe2, 0x82, 0xac]).toString();
 
   assert.throws(
     () => Reflect.get(TextEncoderStream.prototype, 'encoding', {}), {
-      code: 'ERR_INVALID_THIS',
+      name: 'TypeError',
+      message: /Cannot read private member/,
     });
   assert.throws(
     () => Reflect.get(TextEncoderStream.prototype, 'readable', {}), {
-      code: 'ERR_INVALID_THIS',
+      name: 'TypeError',
+      message: /Cannot read private member/,
     });
   assert.throws(
     () => Reflect.get(TextEncoderStream.prototype, 'writable', {}), {
-      code: 'ERR_INVALID_THIS',
+      name: 'TypeError',
+      message: /Cannot read private member/,
     });
 }