diff --git a/ext/objspace/objspace.c b/ext/objspace/objspace.c
index 2784a88e85..72d1eb888d 100644
--- a/ext/objspace/objspace.c
+++ b/ext/objspace/objspace.c
@@ -998,6 +998,7 @@ Init_objspace(void)
      * You can use the #type method to check the type of the internal object.
      */
     rb_cInternalObjectWrapper = rb_define_class_under(rb_mObjSpace, "InternalObjectWrapper", rb_cObject);
+    rb_undef_alloc_func(rb_cInternalObjectWrapper);
     rb_define_method(rb_cInternalObjectWrapper, "type", iow_type, 0);
     rb_define_method(rb_cInternalObjectWrapper, "inspect", iow_inspect, 0);
     rb_define_method(rb_cInternalObjectWrapper, "internal_object_id", iow_internal_object_id, 0);
diff --git a/ext/socket/ifaddr.c b/ext/socket/ifaddr.c
index da013256cb..1da259bd6f 100644
--- a/ext/socket/ifaddr.c
+++ b/ext/socket/ifaddr.c
@@ -460,6 +460,7 @@ rsock_init_sockifaddr(void)
      * Socket::Ifaddr represents a result of getifaddrs() function.
      */
     rb_cSockIfaddr = rb_define_class_under(rb_cSocket, "Ifaddr", rb_cObject);
+    rb_undef_alloc_func(rb_cSockIfaddr);
     rb_define_method(rb_cSockIfaddr, "inspect", ifaddr_inspect, 0);
     rb_define_method(rb_cSockIfaddr, "name", ifaddr_name, 0);
     rb_define_method(rb_cSockIfaddr, "ifindex", ifaddr_ifindex, 0);