diff --git a/niso-ali-1.0.xsd b/niso-ali-1.0.xsd
index 079e234..0e8bb3c 100644
--- a/niso-ali-1.0.xsd
+++ b/niso-ali-1.0.xsd
@@ -4,7 +4,7 @@
   <xsd:element name="free_to_read">
     <xsd:complexType>
       <xsd:attribute name="end_date" use="optional" type="xsd:date"/>
-      <xsd:attribute name="start_date" use="required" type="xsd:date"/>
+      <xsd:attribute name="start_date" use="optional" type="xsd:date"/>
     </xsd:complexType>
   </xsd:element>
   <xsd:element name="license_ref">