diff --git a/include/ruby/backward/classext.h b/include/ruby/backward/classext.h
deleted file mode 100644
index 61d05611bc..0000000000
--- a/include/ruby/backward/classext.h
+++ /dev/null
@@ -1,25 +0,0 @@
-#ifndef RUBY_BACKWARD_CLASSEXT_H                     /*-*-C++-*-vi:se ft=cpp:*/
-#define RUBY_BACKWARD_CLASSEXT_H
-/**
- * @file
- * @author     Ruby developers <ruby-core@ruby-lang.org>
- * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
- *             Permission  is hereby  granted,  to  either redistribute  and/or
- *             modify this file, provided that  the conditions mentioned in the
- *             file COPYING are met.  Consult the file for details.
- */
-#if   defined __GNUC__
-#warning use of RClass internals is deprecated
-#elif defined _MSC_VER
-#pragma message("warning: use of RClass internals is deprecated")
-#endif
-
-typedef struct rb_deprecated_classext_struct {
-    VALUE super;
-} rb_deprecated_classext_t;
-
-#undef RCLASS_SUPER(c)
-#define RCLASS_EXT(c) ((rb_deprecated_classext_t *)RCLASS(c)->ptr)
-#define RCLASS_SUPER(c) (RCLASS(c)->super)
-
-#endif /* RUBY_BACKWARD_CLASSEXT_H */