diff --git a/Userland/Libraries/LibWeb/Fetch/BodyInit.cpp b/Userland/Libraries/LibWeb/Fetch/BodyInit.cpp
index 8dae6b2a20..904b07b4bc 100644
--- a/Userland/Libraries/LibWeb/Fetch/BodyInit.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/BodyInit.cpp
@@ -15,7 +15,7 @@
 namespace Web::Fetch {
 
 // https://fetch.spec.whatwg.org/#concept-bodyinit-extract
-WebIDL::ExceptionOr<Infrastructure::BodyWithType> extract_body(JS::Realm& realm, BodyInit const& object, bool keepalive)
+WebIDL::ExceptionOr<Infrastructure::BodyWithType> extract_body(JS::Realm& realm, BodyInitOrReadbleBytes const& object, bool keepalive)
 {
     auto& window = verify_cast<HTML::Window>(realm.global_object());
 
@@ -49,6 +49,11 @@ WebIDL::ExceptionOr<Infrastructure::BodyWithType> extract_body(JS::Realm& realm,
                 type = blob->type().to_byte_buffer();
             return {};
         },
+        [&](ReadonlyBytes bytes) -> WebIDL::ExceptionOr<void> {
+            // Set source to object.
+            source = TRY_OR_RETURN_OOM(window, ByteBuffer::copy(bytes));
+            return {};
+        },
         [&](JS::Handle<JS::Object> const& buffer_source) -> WebIDL::ExceptionOr<void> {
             // Set source to a copy of the bytes held by object.
             source = TRY_OR_RETURN_OOM(window, WebIDL::get_buffer_source_copy(*buffer_source.cell()));
diff --git a/Userland/Libraries/LibWeb/Fetch/BodyInit.h b/Userland/Libraries/LibWeb/Fetch/BodyInit.h
index 3955a44839..93c390f8b0 100644
--- a/Userland/Libraries/LibWeb/Fetch/BodyInit.h
+++ b/Userland/Libraries/LibWeb/Fetch/BodyInit.h
@@ -19,6 +19,7 @@ using XMLHttpRequestBodyInit = Variant<JS::Handle<FileAPI::Blob>, JS::Handle<JS:
 // https://fetch.spec.whatwg.org/#bodyinit
 using BodyInit = Variant<JS::Handle<Streams::ReadableStream>, JS::Handle<FileAPI::Blob>, JS::Handle<JS::Object>, JS::Handle<URL::URLSearchParams>, String>;
 
-WebIDL::ExceptionOr<Infrastructure::BodyWithType> extract_body(JS::Realm&, BodyInit const&, bool keepalive = false);
+using BodyInitOrReadbleBytes = Variant<JS::Handle<Streams::ReadableStream>, JS::Handle<FileAPI::Blob>, JS::Handle<JS::Object>, JS::Handle<URL::URLSearchParams>, String, ReadonlyBytes>;
+WebIDL::ExceptionOr<Infrastructure::BodyWithType> extract_body(JS::Realm&, BodyInitOrReadbleBytes const&, bool keepalive = false);
 
 }