diff --git a/ChangeLog b/ChangeLog
index 608935e212..9fd567aaad 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Sep  2 22:55:59 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (ISDIGIT): Unused macro removed.
+
 Mon Sep  2 22:49:15 2013  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (str2big_poweroftwo): Extracted from rb_cstr_to_inum.
diff --git a/bignum.c b/bignum.c
index 472126f548..3ea2c4a4c3 100644
--- a/bignum.c
+++ b/bignum.c
@@ -3751,9 +3751,6 @@ rb_cstr_to_inum(const char *str, int base, int badcheck)
     size_t num_digits;
     size_t num_bdigits;
 
-#undef ISDIGIT
-#define ISDIGIT(c) ('0' <= (c) && (c) <= '9')
-
     if (!str) {
 	if (badcheck) goto bad;
 	return INT2FIX(0);