diff --git a/types/whatwg-streams/whatwg-streams-tests.ts b/types/whatwg-streams/whatwg-streams-tests.ts
index c7ed11928b..56246e0d97 100644
--- a/types/whatwg-streams/whatwg-streams-tests.ts
+++ b/types/whatwg-streams/whatwg-streams-tests.ts
@@ -371,11 +371,13 @@ declare class Request {
     readonly url: string;
 }
 declare class Response {
-    constructor(body?: ReadableStream<any>);
-    readonly body: ReadableStream<ArrayBufferView>;
+    constructor(body?: ReadableStream);
+    readonly body: ReadableStream;
 }
 declare class TextDecoderStream extends TransformStream<string, ArrayBufferView> {
 }
+declare class TextEncoderStream extends TransformStream<Uint8Array, string> {
+}
 
 class LipFuzzTransformer implements TransformStreamTransformer<string, string> {
     substitutions: Dictionary<string>;
@@ -439,7 +441,9 @@ class LipFuzzTransformer implements TransformStreamTransformer<string, string> {
                 // Decode the binary-encoded response to string
                 .pipeThrough(new TextDecoderStream())
                 // Apply the LipFuzzTransformer
-                .pipeThrough(ts);
+                .pipeThrough(ts)
+                // Encode the transformed string
+                .pipeThrough(new TextEncoderStream());
             return new Response(transformedBody);
         })
     );