diff --git a/include/pocketpy/interpreter/frame.hpp b/include/pocketpy/interpreter/frame.hpp
index 188f6d81..5f3dc14a 100644
--- a/include/pocketpy/interpreter/frame.hpp
+++ b/include/pocketpy/interpreter/frame.hpp
@@ -19,7 +19,7 @@ struct FastLocals {
     FastLocals(const CodeObject* co, PyVar* a) : co(co), a(a) {}
 
     PyVar* try_get_name(StrName name);
-    NameDict_ to_namedict();
+    NameDict* to_namedict();
 
     PyVar* begin() const { return a; }
 
diff --git a/include/pocketpy/objects/codeobject.hpp b/include/pocketpy/objects/codeobject.hpp
index 3e8ce800..7b850542 100644
--- a/include/pocketpy/objects/codeobject.hpp
+++ b/include/pocketpy/objects/codeobject.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "pocketpy/common/any.h"
+#include "pocketpy/common/traits.hpp"
 #include "pocketpy/objects/tuplelist.hpp"
 #include "pocketpy/objects/namedict.hpp"
 #include "pocketpy/objects/sourcedata.hpp"
@@ -175,15 +176,21 @@ struct NativeFunc {
 };
 
 struct Function {
+    PK_ALWAYS_PASS_BY_POINTER(Function)
+
     FuncDecl_ decl;
     PyObject* _module;  // weak ref
     PyObject* _class;   // weak ref
-    NameDict_ _closure;
+    NameDict* _closure; // strong ref
 
-    explicit Function(FuncDecl_ decl, PyObject* _module, PyObject* _class, NameDict_ _closure) :
+    Function(FuncDecl_ decl, PyObject* _module, PyObject* _class, NameDict* _closure) :
         decl(decl), _module(_module), _class(_class), _closure(_closure) {}
 
     void _gc_mark(VM*) const;
+
+    ~Function() {
+        delete _closure;
+    }
 };
 
 template <typename T>
diff --git a/include/pocketpy/objects/namedict.hpp b/include/pocketpy/objects/namedict.hpp
index d396e35b..3fe57948 100644
--- a/include/pocketpy/objects/namedict.hpp
+++ b/include/pocketpy/objects/namedict.hpp
@@ -59,6 +59,5 @@ struct NameDict {
 };
 
 static_assert(sizeof(NameDict) <= 128);
-using NameDict_ = std::shared_ptr<NameDict>;
 
 }  // namespace pkpy
diff --git a/src/interpreter/ceval.cpp b/src/interpreter/ceval.cpp
index 7a1ff9d6..ad83acb8 100644
--- a/src/interpreter/ceval.cpp
+++ b/src/interpreter/ceval.cpp
@@ -183,11 +183,11 @@ PyVar VM::__run_top_frame() {
                         const FuncDecl_& decl = frame->co->func_decls[byte.arg];
                         PyVar obj;
                         if(decl->nested) {
-                            NameDict_ captured = frame->_locals.to_namedict();
-                            obj = VAR(Function(decl, frame->_module, nullptr, captured));
+                            NameDict* captured = frame->_locals.to_namedict();
+                            obj = new_object<Function>(tp_function, decl, frame->_module, nullptr, captured);
                             captured->set(decl->code->name, obj);
                         } else {
-                            obj = VAR(Function(decl, frame->_module, nullptr, nullptr));
+                            obj = new_object<Function>(tp_function, decl, frame->_module, nullptr, nullptr);
                         }
                         PUSH(obj);
                     }
diff --git a/src/interpreter/frame.cpp b/src/interpreter/frame.cpp
index 71178de6..22e2c8dd 100644
--- a/src/interpreter/frame.cpp
+++ b/src/interpreter/frame.cpp
@@ -8,8 +8,8 @@ PyVar* FastLocals::try_get_name(StrName name) {
     return &a[index];
 }
 
-NameDict_ FastLocals::to_namedict() {
-    NameDict_ dict = std::make_shared<NameDict>();
+NameDict* FastLocals::to_namedict() {
+    NameDict* dict = new NameDict();
     for(int i=0; i<co->varnames_inv.count; i++){
         auto entry = c11__getitem(c11_smallmap_entry_n2i, &co->varnames_inv, i);
         PyVar value = a[entry.value];
diff --git a/src/interpreter/vm.cpp b/src/interpreter/vm.cpp
index f232f135..8804d6f8 100644
--- a/src/interpreter/vm.cpp
+++ b/src/interpreter/vm.cpp
@@ -561,7 +561,7 @@ PyVar VM::__py_exec_internal(const CodeObject_& code, PyVar globals, PyVar local
     PyObject* globals_obj = nullptr;
     Dict* globals_dict = nullptr;
 
-    NameDict_ locals_closure = nullptr;
+    NameDict* locals_closure = nullptr;
     Dict* locals_dict = nullptr;
 
     if(is_none(globals)){
@@ -588,7 +588,7 @@ PyVar VM::__py_exec_internal(const CodeObject_& code, PyVar globals, PyVar local
     } else {
         check_compatible_type(locals, VM::tp_dict);
         locals_dict = &PK_OBJ_GET(Dict, locals);
-        locals_closure = std::make_shared<NameDict>();
+        locals_closure = new NameDict();
         locals_dict->apply([&](PyVar k, PyVar v) {
             locals_closure->set(CAST(Str&, k), v);
         });