diff --git a/ChangeLog b/ChangeLog
index c2b5e87c7b..f53f8ba9b7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun May 29 15:09:05 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* numeric.c (flo_round): fix for negative value.
+
 Sun May 29 02:16:53 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* test/net/http/utils.rb (TestNetHTTPUtils#teardown): add nil check.
diff --git a/bignum.c b/bignum.c
index b8e35c2487..efd4bd3106 100644
--- a/bignum.c
+++ b/bignum.c
@@ -1641,7 +1641,7 @@ rb_big_eql(VALUE x, VALUE y)
  * Unary minus (returns an integer whose value is 0-big)
  */
 
-static VALUE
+VALUE
 rb_big_uminus(VALUE x)
 {
     VALUE z = rb_big_clone(x);
diff --git a/internal.h b/internal.h
index ca4220a841..4e39e47f75 100644
--- a/internal.h
+++ b/internal.h
@@ -25,6 +25,8 @@ struct rb_classext_struct {
     struct st_table *const_tbl;
 };
 
+VALUE rb_big_uminus(VALUE x);
+
 #if defined(__cplusplus)
 #if 0
 { /* satisfy cc-mode */
diff --git a/numeric.c b/numeric.c
index a02dfd3974..fd77ff980a 100644
--- a/numeric.c
+++ b/numeric.c
@@ -97,6 +97,7 @@ round(double x)
 }
 #endif
 
+static VALUE fix_uminus(VALUE num);
 static VALUE fix_mul(VALUE x, VALUE y);
 static VALUE int_pow(long x, unsigned long y);
 
@@ -1504,10 +1505,15 @@ flo_round(int argc, VALUE *argv, VALUE num)
     }
     else {
 	if (ndigits < 0) {
-	    if (fabs(number) < f) return INT2FIX(0);
+	    double absnum = fabs(number);
+	    if (absnum < f) return INT2FIX(0);
 	    if (!FIXABLE(number)) {
 		VALUE f10 = int_pow(10, -ndigits);
-		num = rb_big_idiv(rb_dbl2big(number), f10);
+		VALUE n10 = f10;
+		if (number < 0) {
+		    f10 = FIXNUM_P(f10) ? fix_uminus(f10) : rb_big_uminus(f10);
+		}
+		num = rb_big_idiv(rb_dbl2big(absnum), n10);
 		return FIXNUM_P(num) ? fix_mul(num, f10) : rb_big_mul(num, f10);
 	    }
 	    number /= f;
diff --git a/test/ruby/test_float.rb b/test/ruby/test_float.rb
index 2e879bdd2f..fb37d73831 100644
--- a/test/ruby/test_float.rb
+++ b/test/ruby/test_float.rb
@@ -322,6 +322,7 @@ class TestFloat < Test::Unit::TestCase
     assert_equal(11100.0, 11111.1.round(-2))
 
     assert_equal(10**300, 1.1e300.round(-300))
+    assert_equal(-10**300, -1.1e300.round(-300))
   end
 
   VS = [