diff --git a/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Requests.h b/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Requests.h
index c0261d685d4..03f568bde29 100644
--- a/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Requests.h
+++ b/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Requests.h
@@ -228,6 +228,9 @@ public:
     [[nodiscard]] OriginType const& origin() const { return m_origin; }
     void set_origin(OriginType origin) { m_origin = move(origin); }
 
+    [[nodiscard]] Optional<URL::Origin> const& top_level_navigation_initiator_origin() const { return m_top_level_navigation_initiator_origin; }
+    void set_top_level_navigation_initiator_origin(Optional<URL::Origin> top_level_navigation_initiator_origin) { m_top_level_navigation_initiator_origin = move(top_level_navigation_initiator_origin); }
+
     [[nodiscard]] PolicyContainerType const& policy_container() const { return m_policy_container; }
     void set_policy_container(PolicyContainerType policy_container) { m_policy_container = move(policy_container); }
 
@@ -417,6 +420,10 @@ private:
     // A request has an associated origin, which is "client" or an origin. Unless stated otherwise it is "client".
     OriginType m_origin { Origin::Client };
 
+    // https://fetch.spec.whatwg.org/#request-top-level-navigation-initiator-origin
+    // A request has an associated top-level navigation initiator origin, which is an origin or null. Unless stated otherwise it is null.
+    Optional<URL::Origin> m_top_level_navigation_initiator_origin;
+
     // https://fetch.spec.whatwg.org/#concept-request-policy-container
     // A request has an associated policy container, which is "client" or a policy container. Unless stated otherwise
     // it is "client".
diff --git a/Libraries/LibWeb/HTML/Navigable.cpp b/Libraries/LibWeb/HTML/Navigable.cpp
index 511df6241ec..1062aa373e4 100644
--- a/Libraries/LibWeb/HTML/Navigable.cpp
+++ b/Libraries/LibWeb/HTML/Navigable.cpp
@@ -866,7 +866,10 @@ static WebIDL::ExceptionOr<Navigable::NavigationParamsVariant> create_navigation
     request->set_referrer(entry->document_state()->request_referrer());
     request->set_policy_container(source_snapshot_params.source_policy_container);
 
-    // FIXME: 4. If navigable is a top-level traversable, then set request's top-level navigation initiator origin to entry's document state's initiator origin.
+    // 4. If navigable is a top-level traversable, then set request's top-level navigation initiator origin to entry's
+    //    document state's initiator origin.
+    if (navigable->top_level_traversable()->parent() == nullptr)
+        request->set_top_level_navigation_initiator_origin(entry->document_state()->origin());
 
     // 5. If request's client is null:
     if (request->client() == nullptr) {