diff --git a/ChangeLog b/ChangeLog
index 1c9c39f7dd..3cddc29e8e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Mar  4 15:26:40 2006  Tanaka Akira  <akr@m17n.org>
+
+	* gc.c (id2ref): fix symbol test.
+
 Fri Mar  3 21:22:42 2006  Tanaka Akira  <akr@m17n.org>
 
 	* lib/fileutils.rb (FileUtils.cp_r): implement :remove_destination
diff --git a/gc.c b/gc.c
index 8f4473759c..d3c87ddc8f 100644
--- a/gc.c
+++ b/gc.c
@@ -1938,15 +1938,15 @@ id2ref(VALUE obj, VALUE objid)
     if (ptr == Qfalse) return Qfalse;
     if (ptr == Qnil) return Qnil;
     if (FIXNUM_P(ptr)) return (VALUE)ptr;
+    ptr = objid ^ FIXNUM_FLAG;	/* unset FIXNUM_FLAG */
 
-    if ((objid % sizeof(RVALUE)) == (4 << 2)) {
-        ID symid = objid / sizeof(RVALUE);
+    if ((ptr % sizeof(RVALUE)) == (4 << 2)) {
+        ID symid = ptr / sizeof(RVALUE);
         if (rb_id2name(symid) == 0)
             rb_raise(rb_eRangeError, "%p is not symbol id value", p0);
         return ID2SYM(symid);
     }
 
-    ptr = objid ^ FIXNUM_FLAG;	/* unset FIXNUM_FLAG */
     if (!is_pointer_to_heap((void *)ptr)|| BUILTIN_TYPE(ptr) >= T_BLOCK) {
 	rb_raise(rb_eRangeError, "%p is not id value", p0);
     }
diff --git a/test/ruby/test_objectspace.rb b/test/ruby/test_objectspace.rb
new file mode 100644
index 0000000000..dab94688ee
--- /dev/null
+++ b/test/ruby/test_objectspace.rb
@@ -0,0 +1,35 @@
+require 'test/unit'
+
+class TestObjectSpace < Test::Unit::TestCase
+  def self.deftest_id2ref(obj)
+    /:(\d+)/ =~ caller[0]
+    file = $`
+    line = $1.to_i
+    eval <<"End", binding, file, line
+    define_method("test_id2ref_#{line}") {\
+      o = ObjectSpace._id2ref(obj.object_id);\
+      assert_equal(obj, o, "didn't round trip: #{obj.inspect}");\
+    }
+End
+  end
+
+  deftest_id2ref(-0x4000000000000001)
+  deftest_id2ref(-0x4000000000000000)
+  deftest_id2ref(-0x40000001)
+  deftest_id2ref(-0x40000000)
+  deftest_id2ref(-1)
+  deftest_id2ref(0)
+  deftest_id2ref(1)
+  deftest_id2ref(0x3fffffff)
+  deftest_id2ref(0x40000000)
+  deftest_id2ref(0x3fffffffffffffff)
+  deftest_id2ref(0x4000000000000000)
+  deftest_id2ref(:a)
+  deftest_id2ref(:abcdefghijilkjl)
+  deftest_id2ref(:==)
+  deftest_id2ref(Object.new)
+  deftest_id2ref(self)
+  deftest_id2ref(true)
+  deftest_id2ref(false)
+  deftest_id2ref(nil)
+end