diff --git a/include/pocketpy/interpreter/vm.h b/include/pocketpy/interpreter/vm.h
index 816f760f..d216e612 100644
--- a/include/pocketpy/interpreter/vm.h
+++ b/include/pocketpy/interpreter/vm.h
@@ -67,7 +67,7 @@ typedef struct VM {
     NameDict compile_time_funcs;
 
     py_StackRef curr_class;
-    py_StackRef curr_decl_based_function;
+    py_StackRef curr_decl_based_function;   // this is for get current function without frame
     TraceInfo trace_info;
     WatchdogInfo watchdog_info;
     LineProfiler line_profiler;
diff --git a/src/public/internal.c b/src/public/internal.c
index d7d740af..f291b3d5 100644
--- a/src/public/internal.c
+++ b/src/public/internal.c
@@ -231,6 +231,7 @@ bool pk_loadmethod(py_StackRef self, py_Name name) {
 
     if(ti->getunboundmethod) {
         bool ok = ti->getunboundmethod(self, name);
+        assert(py_retval()->type == tp_nativefunc || py_retval()->type == tp_function);
         if(ok) {
             self[0] = *py_retval();
             self[1] = self_bak;