diff --git a/ChangeLog b/ChangeLog
index b3c3e2d87c..646b4c55b1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat May 31 23:02:00 2008  Tanaka Akira  <akr@fsij.org>
+
+	* gc.c (count_objects): clear given hash.
+
 Sat May 31 20:28:10 2008  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* test/ruby/test_regexp.rb: add tests.
diff --git a/gc.c b/gc.c
index 9bea1240f4..d095c5e8c4 100644
--- a/gc.c
+++ b/gc.c
@@ -2239,6 +2239,15 @@ rb_obj_id(VALUE obj)
     return (VALUE)((SIGNED_VALUE)obj|FIXNUM_FLAG);
 }
 
+static int
+set_zero(st_data_t key, st_data_t val, st_data_t arg)
+{
+    VALUE k = (VALUE)key;
+    VALUE hash = (VALUE)arg;
+    rb_hash_aset(hash, k, INT2FIX(0));
+    return ST_CONTINUE;
+}
+
 /*
  *  call-seq:
  *     ObjectSpace.count_objects([result_hash]) -> hash
@@ -2272,6 +2281,9 @@ count_objects(int argc, VALUE *argv, VALUE os)
     if (rb_scan_args(argc, argv, "01", &hash) == 1) {
         if (TYPE(hash) != T_HASH)
             rb_raise(rb_eTypeError, "non-hash given");
+        if (!RHASH_EMPTY_P(hash)) {
+            st_foreach(RHASH_TBL(hash), set_zero, hash);
+        }
     }
 
     for (i = 0; i <= T_MASK; i++) {
diff --git a/test/ruby/test_objectspace.rb b/test/ruby/test_objectspace.rb
index 6c28d63108..c6fe9f2ef2 100644
--- a/test/ruby/test_objectspace.rb
+++ b/test/ruby/test_objectspace.rb
@@ -47,5 +47,11 @@ End
     assert(h.values.all? {|x| x.is_a?(Integer) })
 
     assert_raise(TypeError) { ObjectSpace.count_objects(1) }
+
+    h0 = {:T_FOO=>1000}
+    h = ObjectSpace.count_objects(h0)
+    p h0.equal?(h)
+    assert_same(h0, h)
+    assert_equal(0, h0[:T_FOO])
   end
 end