diff --git a/include/pocketpy/vm.h b/include/pocketpy/vm.h
index f59dbf57..f8351a59 100644
--- a/include/pocketpy/vm.h
+++ b/include/pocketpy/vm.h
@@ -426,8 +426,8 @@ public:
     PyObject* bind_property(PyObject*, const char*, NativeFuncC fget, NativeFuncC fset=nullptr);
 
     template<typename T>
-    PyObject* register_user_class(PyObject* mod, StrName name, Type base=0, bool subclass_enabled=false){
-        PyObject* type = new_type_object(mod, name, base, subclass_enabled);
+    PyObject* register_user_class(PyObject* mod, StrName name, bool subclass_enabled=false){
+        PyObject* type = new_type_object(mod, name, 0, subclass_enabled);
         mod->attr().set(name, type);
         _cxx_typeid_map[typeid(T)] = PK_OBJ_GET(Type, type);
         T::_register(vm, mod, type);
diff --git a/src/array2d.cpp b/src/array2d.cpp
index 85988ae1..1fc61d6b 100644
--- a/src/array2d.cpp
+++ b/src/array2d.cpp
@@ -373,7 +373,7 @@ struct Array2dIter{
 void add_module_array2d(VM* vm){
     PyObject* mod = vm->new_module("array2d");
 
-    vm->register_user_class<Array2d>(mod, "array2d", 0, true);
+    vm->register_user_class<Array2d>(mod, "array2d", true);
     vm->register_user_class<Array2dIter>(mod, "_array2d_iter");
 
     vm->bind__iter__(vm->_tp_user<Array2d>(), [](VM* vm, PyObject* _0){
diff --git a/src/cffi.cpp b/src/cffi.cpp
index 32dc526d..e869ae44 100644
--- a/src/cffi.cpp
+++ b/src/cffi.cpp
@@ -161,8 +161,8 @@ void add_module_c(VM* vm){
         return vm->None;
     });
 
-    vm->register_user_class<VoidP>(mod, "void_p", 0, true);
-    vm->register_user_class<C99Struct>(mod, "struct", 0, true);
+    vm->register_user_class<VoidP>(mod, "void_p", true);
+    vm->register_user_class<C99Struct>(mod, "struct", true);
     
     mod->attr().set("NULL", VAR_T(VoidP, nullptr));
 
diff --git a/src/collections.cpp b/src/collections.cpp
index c4025d71..d3b4a0ae 100644
--- a/src/collections.cpp
+++ b/src/collections.cpp
@@ -545,7 +545,7 @@ namespace pkpy
     void add_module_collections(VM *vm)
     {
         PyObject *mod = vm->new_module("collections");
-        vm->register_user_class<PyDeque>(mod, "deque", 0, true);
+        vm->register_user_class<PyDeque>(mod, "deque", true);
         vm->register_user_class<PyDequeIter>(mod, "_deque_iter");
         CodeObject_ code = vm->compile(kPythonLibs_collections, "collections.py", EXEC_MODE);
         vm->_exec(code, mod);
diff --git a/src/linalg.cpp b/src/linalg.cpp
index f54e0588..81192c1d 100644
--- a/src/linalg.cpp
+++ b/src/linalg.cpp
@@ -541,10 +541,10 @@ static Vec2 SmoothDamp(Vec2 current, Vec2 target, Vec2& currentVelocity, float s
 void add_module_linalg(VM* vm){
     PyObject* linalg = vm->new_module("linalg");
 
-    vm->register_user_class<Vec2>(linalg, "vec2", 0, true);
-    vm->register_user_class<Vec3>(linalg, "vec3", 0, true);
-    vm->register_user_class<Vec4>(linalg, "vec4", 0, true);
-    vm->register_user_class<Mat3x3>(linalg, "mat3x3", 0, true);
+    vm->register_user_class<Vec2>(linalg, "vec2", true);
+    vm->register_user_class<Vec3>(linalg, "vec3", true);
+    vm->register_user_class<Vec4>(linalg, "vec4", true);
+    vm->register_user_class<Mat3x3>(linalg, "mat3x3", true);
 
     PyObject* float_p = vm->_modules["c"]->attr("float_p");
     linalg->attr().set("vec2_p", float_p);