diff --git a/module/fib.cpp b/module/fib.cpp
index 8d1d69e..68e7264 100644
--- a/module/fib.cpp
+++ b/module/fib.cpp
@@ -47,6 +47,9 @@ struct ghost_obj {
     var test_string = nil;
 };
 
+// if the dynamic library is closed, the pointer of this function will be unsafe
+// make sure gc deletes the object before closing the dynamic library
+// or just do not close the dynamic library...
 void ghost_for_test_destructor(void* ptr) {
     std::cout << "ghost_for_test::destructor (0x";
     std::cout << std::hex << reinterpret_cast<u64>(ptr) << std::dec << ") {\n";
@@ -69,7 +72,7 @@ var create_new_ghost(var* args, usize size, gc* ngc) {
     var res = ngc->alloc(vm_type::vm_ghost);
     res.ghost().set(
         ghost_for_test,
-        nullptr,
+        ghost_for_test_destructor,
         ghost_for_test_gc_marker,
         new ghost_obj
     );
diff --git a/test/module_test.nas b/test/module_test.nas
index 5eec70c..39df4f4 100644
--- a/test/module_test.nas
+++ b/test/module_test.nas
@@ -53,10 +53,10 @@ println("[time  ] ", tm.elapsedMSec()," ms");
 tm.stamp();
 println("[result] ", libfib.qfib(35));
 println("[time  ] ", tm.elapsedMSec()," ms");
-libfib.close();
+# libfib.close();
 println("[result] ", libfib.fib(35));
 println("[result] ", libfib.qfib(35));
-libfib.close();
+# libfib.close();
 
 var speed_test = func() {
     var d = dylib.dlopen("libfib."~(os.platform()=="windows"? "dll":"so"));