diff --git a/ChangeLog b/ChangeLog
index 8aa245f1c5..497131a212 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Jan  3 02:44:34 2008  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (conv_digit): use ISDIGIT, ISLOWER and ISUPPER.
+
 Wed Jan  2 23:50:15 2008  Tanaka Akira  <akr@fsij.org>
 
 	* util.c (ruby_strtoul): "0x", "+" and "-" is not a valid integer.
diff --git a/bignum.c b/bignum.c
index 283a4f4897..227e7a0560 100644
--- a/bignum.c
+++ b/bignum.c
@@ -380,9 +380,9 @@ rb_cstr_to_inum(const char *str, int base, int badcheck)
 
 #define conv_digit(c) \
     (!ISASCII(c) ? -1 : \
-     isdigit(c) ? ((c) - '0') : \
-     islower(c) ? ((c) - 'a' + 10) : \
-     isupper(c) ? ((c) - 'A' + 10) : \
+     ISDIGIT(c) ? ((c) - '0') : \
+     ISLOWER(c) ? ((c) - 'a' + 10) : \
+     ISUPPER(c) ? ((c) - 'A' + 10) : \
      -1)
 
     if (!str) {