diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 07f10b61..40d83bbc 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -83,15 +83,13 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Setup Alpine Linux v3.15 for aarch64
+      - name: Setup Alpine Linux for aarch64
         uses: jirutka/setup-alpine@v1
         with:
           arch: x86
           packages: gcc g++ make cmake libc-dev linux-headers python3
-          branch: v3.15
       - name: Build and Test
         run: |
-          ln -s /usr/bin/python3 /usr/bin/python
           uname -m
           python cmake_build.py
           python scripts/run_tests.py
diff --git a/include/pocketpy/cffi.h b/include/pocketpy/cffi.h
index 8cdd0598..d607ae4c 100644
--- a/include/pocketpy/cffi.h
+++ b/include/pocketpy/cffi.h
@@ -8,17 +8,9 @@ namespace pkpy {
 
 #define PY_CLASS(T, mod, name)                  \
     static Type _type(VM* vm) { return vm->_cxx_typeid_map[&typeid(T)]; }   \
-    static void _check_type(VM* vm, PyObject* val){                         \
-        if(!vm->isinstance(val, T::_type(vm))){                             \
-            vm->TypeError("expected '" #mod "." #name "', got " + _type_name(vm, vm->_tp(val)).escape());  \
-        }                                                                   \
-    }                                                                       \
     static PyObject* register_class(VM* vm, PyObject* mod, Type base=0) {   \
         std::string_view mod_name = PK_OBJ_GET(Str, mod->attr("__name__")).sv();   \
-        if(mod_name != #mod) {                                                     \
-            Str msg = _S("register_class() failed: ", mod_name, " != ", #mod);    \
-            throw std::runtime_error(msg.str());                            \
-        }                                                                   \
+        if(mod_name != #mod) throw std::runtime_error(_S("register_class() failed: ", mod_name, " != ", #mod).str()); \
         PyObject* type = vm->new_type_object(mod, #name, base);             \
         mod->attr().set(#name, type);                                       \
         vm->_cxx_typeid_map[&typeid(T)] = PK_OBJ_GET(Type, type);           \
diff --git a/include/pocketpy/vm.h b/include/pocketpy/vm.h
index 0b6b89c4..bc8ce73b 100644
--- a/include/pocketpy/vm.h
+++ b/include/pocketpy/vm.h
@@ -354,6 +354,11 @@ public:
         TypeError("expected " + _type_name(vm, type).escape() + ", got " + _type_name(vm, _tp(obj)).escape());
     }
 
+    void check_compatible_type(PyObject* obj, Type type){
+        if(isinstance(obj, type)) return;
+        TypeError(_S(_type_name(vm, _tp(obj)).escape(), " is not compatible with ", _type_name(vm, type).escape()));
+    }
+
     PyObject* _t(Type t){
         return _all_types[t.index].obj;
     }
@@ -371,7 +376,10 @@ public:
     struct ImportContext{
         std::vector<Str> pending;
         pod_vector<bool> pending_is_init;   // a.k.a __init__.py
+
         struct Temp{
+            PK_ALWAYS_PASS_BY_POINTER(Temp)
+
             ImportContext* ctx;
             Temp(ImportContext* ctx, Str name, bool is_init) : ctx(ctx){
                 ctx->pending.push_back(name);
@@ -436,7 +444,7 @@ public:
     #elif _MSC_VER
             throw std::runtime_error(__FUNCSIG__ + std::string(" failed: T not found"));
     #else
-            throw std::runtime_error("py_var() failed: T not found");
+            throw std::runtime_error("_find_type_in_cxx_typeid_map() failed: T not found");
     #endif
         }
         return it->second;
@@ -556,7 +564,7 @@ __T _py_cast__internal(VM* vm, PyObject* obj) {
         }
     }
     Type type = vm->_find_type_in_cxx_typeid_map<T>();
-    if constexpr(with_check) vm->check_non_tagged_type(obj, type);
+    if constexpr(with_check) vm->check_compatible_type(obj, type);
     return PK_OBJ_GET(T, obj);
 }