diff --git a/extensions/fetch/22_body.js b/extensions/fetch/22_body.js
index 475af035f7..9b5bf8eff4 100644
--- a/extensions/fetch/22_body.js
+++ b/extensions/fetch/22_body.js
@@ -19,7 +19,7 @@
   const { parseFormData, formDataFromEntries, formDataToBlob } =
     globalThis.__bootstrap.formData;
   const mimesniff = globalThis.__bootstrap.mimesniff;
-  const { isReadableStreamDisturbed, errorReadableStream } =
+  const { isReadableStreamDisturbed, errorReadableStream, createProxy } =
     globalThis.__bootstrap.streams;
 
   class InnerBody {
@@ -133,6 +133,23 @@
       second.length = this.length;
       return second;
     }
+
+    /**
+     * @returns {InnerBody}
+     */
+    createProxy() {
+      let proxyStreamOrStatic;
+      if (this.streamOrStatic instanceof ReadableStream) {
+        proxyStreamOrStatic = createProxy(this.streamOrStatic);
+      } else {
+        proxyStreamOrStatic = { ...this.streamOrStatic };
+        this.streamOrStatic.consumed = true;
+      }
+      const proxy = new InnerBody(proxyStreamOrStatic);
+      proxy.source = this.source;
+      proxy.length = this.length;
+      return proxy;
+    }
   }
 
   /**
diff --git a/extensions/fetch/23_request.js b/extensions/fetch/23_request.js
index ff2bf1d4ea..93d13e8d8d 100644
--- a/extensions/fetch/23_request.js
+++ b/extensions/fetch/23_request.js
@@ -257,14 +257,16 @@
 
       // 28.
       this[_signal] = abortSignal.newSignal();
+
+      // 29.
       if (signal !== null) {
         abortSignal.follow(this[_signal], signal);
       }
 
-      // 29.
+      // 30.
       this[_headers] = headersFromHeaderList(request.headerList, "request");
 
-      // 31.
+      // 32.
       if (Object.keys(init).length > 0) {
         let headers = headerListFromHeaders(this[_headers]).slice(
           0,
@@ -280,13 +282,13 @@
         fillHeaders(this[_headers], headers);
       }
 
-      // 32.
+      // 33.
       let inputBody = null;
       if (input instanceof Request) {
         inputBody = input[_body];
       }
 
-      // 33.
+      // 34.
       if (
         (request.method === "GET" || request.method === "HEAD") &&
         ((init.body !== undefined && init.body !== null) ||
@@ -295,10 +297,10 @@
         throw new TypeError("Request with GET/HEAD method cannot have body.");
       }
 
-      // 34.
+      // 35.
       let initBody = null;
 
-      // 35.
+      // 36.
       if (init.body !== undefined && init.body !== null) {
         const res = extractBody(init.body);
         initBody = res.body;
@@ -307,20 +309,22 @@
         }
       }
 
-      // 36.
+      // 37.
       const inputOrInitBody = initBody ?? inputBody;
 
-      // 38.
-      const finalBody = inputOrInitBody;
-
       // 39.
-      // TODO(lucacasonato): implement this step. Is it needed?
+      let finalBody = inputOrInitBody;
 
       // 40.
-      request.body = finalBody;
+      if (initBody === null && inputBody !== null) {
+        if (input[_body] && input[_body].unusable()) {
+          throw new TypeError("Input request's body is unusable.");
+        }
+        finalBody = inputBody.createProxy();
+      }
 
       // 41.
-      // TODO(lucacasonato): Extranious? https://github.com/whatwg/fetch/issues/1249
+      request.body = finalBody;
     }
 
     get method() {
diff --git a/extensions/web/06_streams.js b/extensions/web/06_streams.js
index be5eca6bad..127436d43a 100644
--- a/extensions/web/06_streams.js
+++ b/extensions/web/06_streams.js
@@ -4246,6 +4246,13 @@
 
   webidl.configurePrototype(WritableStreamDefaultController);
 
+  /**
+   * @param {ReadableStream} stream
+   */
+  function createProxy(stream) {
+    return stream.pipeThrough(new TransformStream());
+  }
+
   webidl.converters.ReadableStream = webidl
     .createInterfaceConverter("ReadableStream", ReadableStream);
   webidl.converters.WritableStream = webidl
@@ -4403,6 +4410,7 @@
     // Non-Public
     isReadableStreamDisturbed,
     errorReadableStream,
+    createProxy,
     // Exposed in global runtime scope
     ByteLengthQueuingStrategy,
     CountQueuingStrategy,
diff --git a/extensions/web/internal.d.ts b/extensions/web/internal.d.ts
index 06976b28bf..bbf529b770 100644
--- a/extensions/web/internal.d.ts
+++ b/extensions/web/internal.d.ts
@@ -81,6 +81,7 @@ declare namespace globalThis {
     declare var streams: {
       ReadableStream: typeof ReadableStream;
       isReadableStreamDisturbed(stream: ReadableStream): boolean;
+      createProxy<T>(stream: ReadableStream<T>): ReadableStream<T>;
     };
 
     declare namespace messagePort {
diff --git a/tools/wpt/expectation.json b/tools/wpt/expectation.json
index 3f30e9ca9c..94d9ea81cd 100644
--- a/tools/wpt/expectation.json
+++ b/tools/wpt/expectation.json
@@ -700,11 +700,7 @@
     "api": {
       "request": {
         "request-init-002.any.html": true,
-        "request-init-stream.any.html": [
-          "Constructing a Request with a Request on which body.getReader() is called",
-          "Constructing a Request with a Request on which body.getReader().read() is called",
-          "Constructing a Request with a Request on which read() and releaseLock() are called"
-        ],
+        "request-init-stream.any.html": true,
         "request-consume-empty.any.html": [
           "Consume empty FormData request body as text"
         ],