diff --git a/step-message/src/main/xml/specification.xml b/step-message/src/main/xml/specification.xml
index 898557e..775d8ac 100644
--- a/step-message/src/main/xml/specification.xml
+++ b/step-message/src/main/xml/specification.xml
@@ -89,7 +89,7 @@ A machine-readable description of this step may be found in
   <p:input port="source" sequence="true"/>
   <p:output port="result" sequence="true"/>
   <p:option name="test" as="xs:boolean" select="true()"/>
-  <p:option name="select" as="xs:string"/>
+  <p:option name="select" as="xs:string" required="true"/>
 </p:declare-step>
 
 <para>Steps that produce messages offer one way for an author to keep track of