diff --git a/dln.h b/dln.h
index d8999635bc..99106fd22b 100644
--- a/dln.h
+++ b/dln.h
@@ -13,22 +13,6 @@
 
 #include "ruby/defines.h"       /* for RUBY_SYMBOL_EXPORT_BEGIN */
 
-#ifdef __cplusplus
-# ifndef  HAVE_PROTOTYPES
-#  define HAVE_PROTOTYPES 1
-# endif
-# ifndef  HAVE_STDARG_PROTOTYPES
-#  define HAVE_STDARG_PROTOTYPES 1
-# endif
-#endif
-
-#undef _
-#ifdef HAVE_PROTOTYPES
-# define _(args) args
-#else
-# define _(args) ()
-#endif
-
 RUBY_SYMBOL_EXPORT_BEGIN
 
 #ifndef DLN_FIND_EXTRA_ARG