diff --git a/src/rgw/rgw_rados.cc b/src/rgw/rgw_rados.cc
index 2b543d95b81db..3d0eb6a274d4b 100644
--- a/src/rgw/rgw_rados.cc
+++ b/src/rgw/rgw_rados.cc
@@ -4152,9 +4152,10 @@ int RGWRados::copy_obj(RGWObjectCtx& obj_ctx,
     vector<rgw_raw_obj>::iterator riter;
 
     /* rollback reference */
+    string ref_tag = tag + '\0';
     for (riter = ref_objs.begin(); riter != ref_objs.end(); ++riter) {
       ObjectWriteOperation op;
-      cls_refcount_put(op, tag, true);
+      cls_refcount_put(op, ref_tag, true);
 
       ref.pool.ioctx().locator_set_key(riter->loc);