diff --git a/widget/gtk/mozwayland/mozwayland.c b/widget/gtk/mozwayland/mozwayland.c
--- a/widget/gtk/mozwayland/mozwayland.c
+++ b/widget/gtk/mozwayland/mozwayland.c
@@ -200,3 +200,10 @@
 
 MOZ_EXPORT void wl_list_insert_list(struct wl_list* list,
                                     struct wl_list* other) {}
+
+MOZ_EXPORT struct wl_proxy* wl_proxy_marshal_flags(
+    struct wl_proxy* proxy, uint32_t opcode,
+    const struct wl_interface* interface, uint32_t version, uint32_t flags,
+    ...) {
+  return NULL;
+}