diff --git a/Userland/Libraries/LibWeb/Fetch/BodyInit.h b/Userland/Libraries/LibWeb/Fetch/BodyInit.h
index 24dc2f244c..cd2be22857 100644
--- a/Userland/Libraries/LibWeb/Fetch/BodyInit.h
+++ b/Userland/Libraries/LibWeb/Fetch/BodyInit.h
@@ -16,6 +16,9 @@ namespace Web::Fetch {
 // https://fetch.spec.whatwg.org/#typedefdef-xmlhttprequestbodyinit
 using XMLHttpRequestBodyInit = Variant<JS::Handle<FileAPI::Blob>, JS::Handle<JS::Object>, JS::Handle<URL::URLSearchParams>, String>;
 
+// 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>;
+
 ErrorOr<Infrastructure::BodyWithType> extract_body(JS::Realm&, XMLHttpRequestBodyInit const&);
 
 }
diff --git a/Userland/Libraries/LibWeb/Fetch/BodyInit.idl b/Userland/Libraries/LibWeb/Fetch/BodyInit.idl
index 15f001a8a8..d57d42bffb 100644
--- a/Userland/Libraries/LibWeb/Fetch/BodyInit.idl
+++ b/Userland/Libraries/LibWeb/Fetch/BodyInit.idl
@@ -1,5 +1,11 @@
 #import <FileAPI/Blob.idl>
+#import <Streams/ReadableStream.idl>
 #import <URL/URLSearchParams.idl>
 
 // https://fetch.spec.whatwg.org/#typedefdef-xmlhttprequestbodyinit
 typedef (Blob or BufferSource or URLSearchParams or USVString) XMLHttpRequestBodyInit;
+
+// https://fetch.spec.whatwg.org/#bodyinit
+// FIXME: IDLParser doesn't resolve nested unions properly
+// typedef (ReadableStream or XMLHttpRequestBodyInit) BodyInit;
+typedef (ReadableStream or Blob or BufferSource or URLSearchParams or USVString) BodyInit;