diff --git a/ChangeLog b/ChangeLog
index 4e8fa65845..fd4eb82ba0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Tue Oct  9 17:59:00 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* random.c (rb_random_ulong_limited): new function to return a random
+	  value from 0 upto limit as unsigned long, simillary to
+	  rb_genrand_ulong_limited but with arbitrary RNG object.
+
 Tue Oct  9 17:13:27 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* process.c (rb_execarg_addopt, rb_execarg_run_options): add :uid and
diff --git a/include/ruby/intern.h b/include/ruby/intern.h
index eebb24ce0a..f954232b48 100644
--- a/include/ruby/intern.h
+++ b/include/ruby/intern.h
@@ -610,6 +610,7 @@ VALUE rb_random_bytes(VALUE rnd, long n);
 VALUE rb_random_int(VALUE rnd, VALUE max);
 unsigned int rb_random_int32(VALUE rnd);
 double rb_random_real(VALUE rnd);
+unsigned long rb_random_ulong_limited(VALUE rnd, unsigned long limit);
 unsigned long rb_genrand_ulong_limited(unsigned long i);
 /* re.c */
 #define rb_memcmp memcmp
diff --git a/random.c b/random.c
index b36784c405..ccae2a0178 100644
--- a/random.c
+++ b/random.c
@@ -943,6 +943,22 @@ rb_random_real(VALUE obj)
     return genrand_real(&rnd->mt);
 }
 
+unsigned long
+rb_random_ulong_limited(VALUE obj, unsigned long limit)
+{
+    rb_random_t *rnd = try_get_rnd(obj);
+    if (!rnd) {
+	VALUE lim = ULONG2NUM(limit);
+	VALUE v = rb_funcall2(obj, id_rand, 1, &lim);
+	unsigned long r = NUM2ULONG(v);
+	if (r > limit) {
+	    rb_raise(rb_eRangeError, "random number too big %ld", r);
+	}
+	return r;
+    }
+    return limited_rand(&rnd->mt, limit);
+}
+
 /*
  * call-seq: prng.bytes(size) -> a_string
  *