diff --git a/src/current/calc.xsd b/src/current/calc.xsd
index ac1b49f1..d7283795 100644
--- a/src/current/calc.xsd
+++ b/src/current/calc.xsd
@@ -44,7 +44,7 @@
 
     <!-- we need to allow '@' since that's used in macros -->
     <xs:restriction base="xs:string">
-      <xs:pattern value="[a-zA-Z_@{-][a-zA-Z0-9_@{}-]*" />
+      <xs:pattern value="#[0-9]+|[a-zA-Z_@{-][a-zA-Z0-9_@{}-]*" />
       <xs:maxLength value="50" />
     </xs:restriction>
   </xs:simpleType>