diff --git a/namespace.c b/namespace.c
index b85cbf5715..4e5a4e9bc4 100644
--- a/namespace.c
+++ b/namespace.c
@@ -268,7 +268,7 @@ const rb_data_type_t rb_root_namespace_data_type = {
         namespace_entry_memsize,
         rb_namespace_gc_update_references,
     },
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY // TODO: enable RUBY_TYPED_WB_PROTECTED when inserting write barriers
+    &rb_namespace_data_type, 0, RUBY_TYPED_FREE_IMMEDIATELY // TODO: enable RUBY_TYPED_WB_PROTECTED when inserting write barriers
 };
 
 VALUE