diff --git a/trytond/ir/ui/calendar.rnc b/trytond/ir/ui/calendar.rnc
index da16cad0a8..66d7082a6d 100644
--- a/trytond/ir/ui/calendar.rnc
+++ b/trytond/ir/ui/calendar.rnc
@@ -18,7 +18,7 @@ data = element data { attlist.data, xpath* }
 attlist.data &= empty
 
 xpath = element xpath {
-    attlist.xpath, ( field )*
+    attlist.xpath, (field | calendar)*
   }
 attlist.xpath &= attribute expr { text }
 attlist.xpath &=
diff --git a/trytond/ir/ui/calendar.rng b/trytond/ir/ui/calendar.rng
index 800d86ce7a..bec99ace80 100644
--- a/trytond/ir/ui/calendar.rng
+++ b/trytond/ir/ui/calendar.rng
@@ -60,7 +60,10 @@
     <element name="xpath">
       <ref name="attlist.xpath"/>
       <zeroOrMore>
-        <ref name="field"/>
+        <choice>
+          <ref name="field"/>
+          <ref name="calendar"/>
+        </choice>
       </zeroOrMore>
     </element>
   </define>