diff --git a/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.cpp b/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.cpp
index d2fe96fe05..dcea6abadd 100644
--- a/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.cpp
+++ b/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.cpp
@@ -39,7 +39,7 @@ void ReadableStreamBYOBRequest::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_view);
 }
 
-WebIDL::ExceptionOr<void> ReadableStreamBYOBRequest::respond(u64 bytes_written)
+WebIDL::ExceptionOr<void> ReadableStreamBYOBRequest::respond(WebIDL::UnsignedLongLong bytes_written)
 {
     // 1. If this.[[controller]] is undefined, throw a TypeError exception.
     if (!m_controller)
diff --git a/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.h b/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.h
index 6f651e9169..f5a6007b5f 100644
--- a/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.h
+++ b/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.h
@@ -11,6 +11,7 @@
 #include <LibWeb/Bindings/PlatformObject.h>
 #include <LibWeb/Forward.h>
 #include <LibWeb/Streams/ReadableByteStreamController.h>
+#include <LibWeb/WebIDL/Types.h>
 
 namespace Web::Streams {
 
@@ -28,7 +29,7 @@ public:
 
     void set_view(JS::GCPtr<WebIDL::ArrayBufferView> value) { m_view = value; }
 
-    WebIDL::ExceptionOr<void> respond(u64 bytes_written);
+    WebIDL::ExceptionOr<void> respond(WebIDL::UnsignedLongLong bytes_written);
 
 private:
     explicit ReadableStreamBYOBRequest(JS::Realm&);
diff --git a/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.idl b/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.idl
index a84671a484..36ce9d8d62 100644
--- a/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.idl
+++ b/Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.idl
@@ -3,7 +3,6 @@
 interface ReadableStreamBYOBRequest {
     readonly attribute ArrayBufferView? view;
 
-    // FIXME: Should be unsigned long long
-    undefined respond([EnforceRange] unsigned long bytesWritten);
+    undefined respond([EnforceRange] unsigned long long bytesWritten);
     // FIXME: undefined respondWithNewView(ArrayBufferView view);
 };