diff --git a/extlib/benz/include/picrin/config.h b/extlib/benz/include/picrin/config.h
index 867f33e2..e928f95f 100644
--- a/extlib/benz/include/picrin/config.h
+++ b/extlib/benz/include/picrin/config.h
@@ -2,43 +2,26 @@
  * See Copyright Notice in picrin.h
  */
 
-/** switch normal VM and direct threaded VM */
-/* #define PIC_DIRECT_THREADED_VM 1 */
-
-/** switch internal value representation */
-/* #define PIC_NAN_BOXING 1 */
-
 /** no dependency on libc */
 /* #define PIC_ENABLE_LIBC 1 */
 
 /** use stdio or not */
 /* #define PIC_ENABLE_STDIO 1 */
 
-/** custom setjmp/longjmp */
+/** essential external functions */
 /* #define PIC_JMPBUF jmp_buf */
 /* #define PIC_SETJMP(pic, buf) setjmp(buf) */
 /* #define PIC_LONGJMP(pic, buf, val) longjmp((buf), (val)) */
-
-/** custom abort */
 /* #define PIC_ABORT(pic) abort() */
 
 /** initial memory size (to be dynamically extended if necessary) */
 /* #define PIC_ARENA_SIZE 1000 */
-
 /* #define PIC_HEAP_PAGE_SIZE 10000 */
-
 /* #define PIC_PAGE_REQUEST_THRESHOLD(total) ((total) * 77 / 100) */
-
 /* #define PIC_STACK_SIZE 1024 */
-
 /* #define PIC_RESCUE_SIZE 30 */
-
 /* #define PIC_SYM_POOL_SIZE 128 */
-
 /* #define PIC_IREP_SIZE 8 */
-
 /* #define PIC_POOL_SIZE 8 */
-
 /* #define PIC_SYMS_SIZE 32 */
-
 /* #define PIC_ISEQ_SIZE 1024 */
diff --git a/extlib/benz/include/picrin/setup.h b/extlib/benz/include/picrin/setup.h
index 34e36a49..86aee1b2 100644
--- a/extlib/benz/include/picrin/setup.h
+++ b/extlib/benz/include/picrin/setup.h
@@ -4,18 +4,6 @@
 
 #include "picrin/config.h"
 
-#ifndef PIC_DIRECT_THREADED_VM
-# if (defined(__GNUC__) || defined(__clang__)) && ! defined(__STRICT_ANSI__)
-#  define PIC_DIRECT_THREADED_VM 1
-# endif
-#endif
-
-#ifndef PIC_NAN_BOXING
-# if __x86_64__ && (defined(__GNUC__) || defined(__clang__)) && ! defined(__STRICT_ANSI__)
-#  define PIC_NAN_BOXING 1
-# endif
-#endif
-
 #ifndef PIC_ENABLE_LIBC
 # define PIC_ENABLE_LIBC 1
 #endif
@@ -457,3 +445,17 @@ void PIC_DOUBLE_TO_CSTRING(double, char *);
 #define PIC_CSTRING_TO_DOUBLE atof
 #endif
 double PIC_CSTRING_TO_DOUBLE(const char *);
+
+/* optional features available? */
+
+#if (defined(__GNUC__) || defined(__clang__)) && ! defined(__STRICT_ANSI__)
+# define PIC_DIRECT_THREADED_VM 1
+#else
+# define PIC_DIRECT_THREADED_VM 0
+#endif
+
+#if __x86_64__ && (defined(__GNUC__) || defined(__clang__)) && ! defined(__STRICT_ANSI__)
+# define PIC_NAN_BOXING 1
+#else
+# define PIC_NAN_BOXING 0
+#endif