diff --git a/ChangeLog b/ChangeLog
index 329aeef870..29b800fd62 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Oct 30 19:28:02 2006  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* bignum.c (rb_big2str0): use better approximation.
+
 Mon Oct 30 18:35:33 2006  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* bignum.c (rb_big2str0): wrong allocation length.  a patch from
diff --git a/bignum.c b/bignum.c
index 0bfeffaa52..f0c3a0f63a 100644
--- a/bignum.c
+++ b/bignum.c
@@ -598,7 +598,7 @@ rb_big2str0(VALUE x, int base, int trim)
     switch (base) {
       case 2: break;
       case 3:
-	j = j * 647L / 1024;
+	j = j * 53L / 84 + 1;
 	break;
       case 4: case 5: case 6: case 7:
 	j /= 2;
@@ -607,7 +607,7 @@ rb_big2str0(VALUE x, int base, int trim)
 	j /= 3;
 	break;
       case 10: case 11: case 12: case 13: case 14: case 15:
-	j = j * 241L / 800 + 1;
+	j = j * 28L / 93 + 1;
 	break;
       case 16: case 17: case 18: case 19: case 20: case 21:
       case 22: case 23: case 24: case 25: case 26: case 27: