diff --git a/src/current/calc.xsd b/src/current/calc.xsd
index d7283795..c2e220db 100644
--- a/src/current/calc.xsd
+++ b/src/current/calc.xsd
@@ -718,6 +718,7 @@
     <xs:sequence>
       <xs:element name="when" type="whenType" minOccurs="0" maxOccurs="unbounded" />
       <xs:element name="index" type="indexType" minOccurs="0" maxOccurs="2" />
+      <xs:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded" />
     </xs:sequence>
 
     <xs:attribute name="value" type="constValueType" use="required">