diff --git a/ChangeLog b/ChangeLog
index c80eeb594f..5642e5d5a1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Dec 19 10:50:13 2013  Koichi Sasada  <ko1@atdot.net>
+
+	* gc.c (newobj_of): don't need to RBASIC_SET_CLASS() which includes WB
+	  here because created obj is always YOUNG/INFANT.
+
 Thu Dec 19 10:48:37 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* benchmark/gc/gcbench.rb: check GC::OPTS availability
diff --git a/gc.c b/gc.c
index 3082956b8f..80ec4a3e88 100644
--- a/gc.c
+++ b/gc.c
@@ -1291,7 +1291,7 @@ newobj_of(VALUE klass, VALUE flags, VALUE v1, VALUE v2, VALUE v3)
 
     /* OBJSETUP */
     RBASIC(obj)->flags = flags;
-    RBASIC_SET_CLASS(obj, klass);
+    RBASIC_SET_CLASS_RAW(obj, klass);
     if (rb_safe_level() >= 3) FL_SET((obj), FL_TAINT);
     RANY(obj)->as.values.v1 = v1;
     RANY(obj)->as.values.v2 = v2;