diff --git a/ChangeLog b/ChangeLog
index f58ecf9a30..1a3c4aaebd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Jul 16 22:50:41 2012  Tanaka Akira  <akr@fsij.org>
+
+	* numeric.c (flo_to_s): use the exponential form if the integer part
+	  is longer than or equal DBL_DIG.
+	  [ruby-dev:45960] [ruby-trunk - Bug #6741]
+
 Mon Jul 16 22:01:00 2012  Ayumu AIZAWA  <ayumu.aizawa@gmail.com>
 
 	* ext/readline/readline.c: fixed docs. [Bug #6740][ruby-core:46501]
diff --git a/numeric.c b/numeric.c
index b40f0695b8..73626e1c05 100644
--- a/numeric.c
+++ b/numeric.c
@@ -662,7 +662,7 @@ flo_to_s(VALUE flt)
 	    buf[decpt] = '.';
 	    rb_str_cat(s, buf, digs + 1);
 	}
-	else if (decpt - digs < float_dig) {
+	else if (decpt <= DBL_DIG) {
 	    long len;
 	    char *ptr;
 	    rb_str_cat(s, buf, digs);