diff --git a/openerp/addons/base/rng/view.rng b/openerp/addons/base/rng/view.rng
index de0af811b83..5febbf2948c 100644
--- a/openerp/addons/base/rng/view.rng
+++ b/openerp/addons/base/rng/view.rng
@@ -663,6 +663,7 @@
             <rng:optional><rng:attribute name="string" /></rng:optional>
             <rng:optional><rng:attribute name="orientation" /></rng:optional>
             <rng:optional><rng:attribute name="type" /></rng:optional>
+            <rng:optional><rng:attribute name="stacked" /></rng:optional>
             <rng:optional><rng:attribute name="color"/></rng:optional>
             <rng:oneOrMore>
                 <rng:ref name="field"/>