diff --git a/ChangeLog b/ChangeLog
index b0eb53c843..18c0f8b7af 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jun 12 07:32:01 2013  Tanaka Akira  <akr@fsij.org>
+
+	* random.c (rand_int): Use rb_big_uminus.
+
 Wed Jun 12 07:12:54 2013  Eric Hodel  <drbrain@segment7.net>
 
 	* struct.c:  Improve documentation: replace "instance variable" with
diff --git a/random.c b/random.c
index 4175e94b44..61262fb4db 100644
--- a/random.c
+++ b/random.c
@@ -946,8 +946,7 @@ rand_int(struct MT *mt, VALUE vmax, int restrictive)
 	if (rb_bigzero_p(vmax)) return Qnil;
 	if (!RBIGNUM_SIGN(vmax)) {
 	    if (restrictive) return Qnil;
-	    vmax = rb_big_clone(vmax);
-	    RBIGNUM_SET_SIGN(vmax, 1);
+            vmax = rb_big_uminus(vmax);
 	}
 	vmax = rb_big_minus(vmax, INT2FIX(1));
 	if (FIXNUM_P(vmax)) {