diff --git a/gc/gc.h b/gc/gc.h
index d38a129..31ce736 100644
--- a/gc/gc.h
+++ b/gc/gc.h
@@ -86,9 +86,7 @@ MODULAR_GC_FN void rb_gc_mark_roots(void *objspace, const char **categoryp);
 MODULAR_GC_FN void rb_gc_ractor_newobj_cache_foreach(void (*func)(void *cache, void *data), void *data);
 MODULAR_GC_FN bool rb_gc_multi_ractor_p(void);
 MODULAR_GC_FN bool rb_gc_shutdown_call_finalizer_p(VALUE obj);
-MODULAR_GC_FN uint32_t rb_gc_get_shape(VALUE obj);
-MODULAR_GC_FN void rb_gc_set_shape(VALUE obj, uint32_t shape_id);
-MODULAR_GC_FN uint32_t rb_gc_rebuild_shape(VALUE obj, size_t heap_id);
+MODULAR_GC_FN void rb_gc_obj_changed_pool(VALUE obj, size_t heap_id);
 MODULAR_GC_FN void rb_gc_prepare_heap_process_object(VALUE obj);
 MODULAR_GC_FN bool rb_memerror_reentered(void);
 MODULAR_GC_FN bool rb_obj_id_p(VALUE);
diff --git a/gc/mmtk/mmtk.c b/gc/mmtk/mmtk.c
index e4cd719..9b1aed4 100644
--- a/gc/mmtk/mmtk.c
+++ b/gc/mmtk/mmtk.c
@@ -16,6 +16,22 @@
 #include <sys/sysctl.h>
 #endif
 
+#ifndef VM_CHECK_MODE
+# define VM_CHECK_MODE RUBY_DEBUG
+#endif
+
+// From ractor_core.h
+#ifndef RACTOR_CHECK_MODE
+# define RACTOR_CHECK_MODE (VM_CHECK_MODE || RUBY_DEBUG) && (SIZEOF_UINT64_T == SIZEOF_VALUE)
+#endif
+
+#if RACTOR_CHECK_MODE
+# define RVALUE_SUFFIX_SIZE sizeof(VALUE)
+void rb_ractor_setup_belonging(VALUE obj);
+#else
+# define RVALUE_SUFFIX_SIZE 0
+#endif
+
 struct objspace {
     bool measure_gc_time;
     bool gc_stress;
@@ -557,7 +573,11 @@ void *
 rb_gc_impl_objspace_alloc(void)
 {
     MMTk_Builder *builder = rb_mmtk_builder_init();
-    mmtk_init_binding(builder, NULL, &ruby_upcalls);
+    MMTk_RubyBindingOptions binding_options = {
+        .ractor_check_mode = RACTOR_CHECK_MODE != 0,
+        .suffix_size = RVALUE_SUFFIX_SIZE,
+    };
+    mmtk_init_binding(builder, &binding_options, &ruby_upcalls);
 
     return calloc(1, sizeof(struct objspace));
 }
@@ -885,7 +905,8 @@ rb_gc_impl_new_obj(void *objspace_ptr, void *cache_ptr, VALUE klass, VALUE flags
         mmtk_handle_user_collection_request(ractor_cache, false, false);
     }
 
-    alloc_size += sizeof(VALUE);
+    // Layout: [hidden size header (sizeof(VALUE))][payload (alloc_size)][suffix (RVALUE_SUFFIX_SIZE)]
+    alloc_size += sizeof(VALUE) + RVALUE_SUFFIX_SIZE;
 
     VALUE *alloc_obj = (VALUE *)rb_mmtk_alloc_fast_path(objspace, ractor_cache, alloc_size);
     if (!alloc_obj) {
@@ -893,7 +914,7 @@ rb_gc_impl_new_obj(void *objspace_ptr, void *cache_ptr, VALUE klass, VALUE flags
     }
 
     alloc_obj++;
-    alloc_obj[-1] = alloc_size - sizeof(VALUE);
+    alloc_obj[-1] = alloc_size - sizeof(VALUE) - RVALUE_SUFFIX_SIZE;
     alloc_obj[0] = flags;
     alloc_obj[1] = klass;
 
@@ -905,6 +926,10 @@ rb_gc_impl_new_obj(void *objspace_ptr, void *cache_ptr, VALUE klass, VALUE flags
 
     objspace->total_allocated_objects++;
 
+#if RACTOR_CHECK_MODE
+    rb_ractor_setup_belonging((VALUE)alloc_obj);
+#endif
+
     return (VALUE)alloc_obj;
 }
 
diff --git a/gc/mmtk/mmtk.h b/gc/mmtk/mmtk.h
index ee338c8..e8f9592 100644
--- a/gc/mmtk/mmtk.h
+++ b/gc/mmtk/mmtk.h
@@ -95,7 +95,7 @@ bool mmtk_is_reachable(MMTk_ObjectReference object);
 MMTk_Builder *mmtk_builder_default(void);
 
 void mmtk_init_binding(MMTk_Builder *builder,
-                       const struct MMTk_RubyBindingOptions *_binding_options,
+                       const struct MMTk_RubyBindingOptions *binding_options,
                        const struct MMTk_RubyUpcalls *upcalls);
 
 void mmtk_initialize_collection(MMTk_VMThread tls);
diff --git a/gc/mmtk/src/api.rs b/gc/mmtk/src/api.rs
index b9797f6..1519d2b 100644
--- a/gc/mmtk/src/api.rs
+++ b/gc/mmtk/src/api.rs
@@ -181,7 +181,7 @@ pub extern "C" fn mmtk_builder_default() -> *mut MMTKBuilder {
 #[no_mangle]
 pub unsafe extern "C" fn mmtk_init_binding(
     builder: *mut MMTKBuilder,
-    _binding_options: *const RubyBindingOptions,
+    binding_options: *const RubyBindingOptions,
     upcalls: *const RubyUpcalls,
 ) {
     crate::MUTATOR_THREAD_PANIC_HANDLER
@@ -191,10 +191,7 @@ pub unsafe extern "C" fn mmtk_init_binding(
     crate::set_panic_hook();
 
     let builder: Box<MMTKBuilder> = unsafe { Box::from_raw(builder) };
-    let binding_options = RubyBindingOptions {
-        ractor_check_mode: false,
-        suffix_size: 0,
-    };
+    let binding_options = unsafe { (*binding_options).clone() };
     let mmtk_boxed = mmtk_init(&builder);
     let mmtk_static = Box::leak(Box::new(mmtk_boxed));