diff --git a/ChangeLog b/ChangeLog
index 5d9806d088..bdd3a79e46 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed May 12 16:43:12 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* numeric.c (flo_to_s): fixed broken output including nuls.
+
 Wed May 12 16:25:46 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* numeric.c (flo_to_s): exponent needs 2 digits.
diff --git a/numeric.c b/numeric.c
index d6dd1c4a5c..00d670b70f 100644
--- a/numeric.c
+++ b/numeric.c
@@ -585,10 +585,15 @@ flo_to_s(VALUE flt)
 	}
 	else if (decpt - digs < float_dig) {
 	    long len;
+	    char *ptr;
 	    rb_str_cat(s, buf, digs);
 	    rb_str_resize(s, (len = RSTRING_LEN(s)) + decpt - digs + 2);
-	    if (decpt > digs) memset(RSTRING_PTR(s) + len, '0', decpt - digs);
-	    rb_str_cat(s, ".0", 2);
+	    ptr = RSTRING_PTR(s) + len;
+	    if (decpt > digs) {
+		memset(ptr, '0', decpt - digs);
+		ptr += decpt - digs;
+	    }
+	    memcpy(ptr, ".0", 2);
 	}
 	else {
 	    goto exp;