diff --git a/trytond/ir/ui/tree.dtd b/trytond/ir/ui/tree.dtd
index 751424b487..81a82650f3 100644
--- a/trytond/ir/ui/tree.dtd
+++ b/trytond/ir/ui/tree.dtd
@@ -14,6 +14,7 @@
 <!ATTLIST field tree_invisible (0|1) "0">
 <!ATTLIST field icon CDATA #IMPLIED>
 <!ATTLIST field sum CDATA #IMPLIED>
+<!ATTLIST field width CDATA #IMPLIED>
 <!ELEMENT data (xpath+)>
 <!ELEMENT xpath ANY>
 <!ATTLIST xpath expr CDATA #REQUIRED>