diff --git a/ext/v8/v8_weakref.cpp b/ext/v8/v8_weakref.cpp
index 919c84b..2ff949f 100644
--- a/ext/v8/v8_weakref.cpp
+++ b/ext/v8/v8_weakref.cpp
@@ -5,19 +5,33 @@ using namespace v8;
 
 v8_weakref::v8_weakref(VALUE object) {
   this->external = Persistent<External>::New(External::New((void *)this));
-  this->external.MakeWeak(this, v8_weakref_finalize);
+  this->external.MakeWeak(this, v8_weakref_dispose);
   this->set(object);
 }
 
 void v8_weakref::set(VALUE value) {
   this->object_id = rb_obj_id(value);
+  VALUE self = Data_Wrap_Struct(rb_cObject, 0, 0, this);
+  VALUE finalizer = rb_proc_new((VALUE (*)(...))v8_weakref_finalize, self);
+  rb_funcall(v8_weakref_objectspace(), rb_intern("define_finalizer"), 2, value, finalizer);
 }
 
 VALUE v8_weakref::get() {
-  return rb_rescue((VALUE (*)(...))v8_weakref_id2ref, this->object_id, (VALUE (*)(...))v8_weakref_nil, Qnil);
+  if (this->object_id) {
+    return rb_rescue((VALUE (*)(...))v8_weakref_id2ref, this->object_id, (VALUE (*)(...))v8_weakref_nil, Qnil);
+  } else {
+    return Qnil;
+  }
 }
 
-void v8_weakref_finalize(Persistent<Value> value, void* weakref) {
+VALUE v8_weakref_finalize(VALUE self, VALUE object_id) {
+  v8_weakref* weakref = 0;
+  Data_Get_Struct(self, struct v8_weakref, weakref);
+  weakref->object_id = Qnil;
+  return Qnil;
+}
+
+void v8_weakref_dispose(Persistent<Value> value, void* weakref) {
   value.Dispose();
   value.Clear();
   delete (v8_weakref*)weakref;
@@ -27,7 +41,11 @@ VALUE v8_weakref_nil(VALUE nil, VALUE exception) {
   return nil;
 }
 
-VALUE v8_weakref_id2ref(VALUE id) {
-  return rb_funcall(rb_const_get(rb_cObject, rb_intern("ObjectSpace")), rb_intern("_id2ref"), 1, id);
+VALUE v8_weakref_objectspace() {
+  return rb_const_get(rb_cObject, rb_intern("ObjectSpace"));
+}
+
+VALUE v8_weakref_id2ref(VALUE id) {
+  return rb_funcall(v8_weakref_objectspace(), rb_intern("_id2ref"), 1, id);
 }
 
diff --git a/ext/v8/v8_weakref.h b/ext/v8/v8_weakref.h
index 21c1218..3aa3091 100644
--- a/ext/v8/v8_weakref.h
+++ b/ext/v8/v8_weakref.h
@@ -15,7 +15,9 @@ struct v8_weakref  {
   v8::Persistent<v8::External> external;
 };
 
-void  v8_weakref_finalize(v8::Persistent<v8::Value> value, void* weakref);
+void  v8_weakref_dispose(v8::Persistent<v8::Value> value, void* weakref);
+VALUE v8_weakref_finalize(VALUE self, VALUE object_id);
+VALUE v8_weakref_objectspace();
 VALUE v8_weakref_nil(VALUE nil, VALUE exception);
 VALUE v8_weakref_id2ref(VALUE id);