diff --git a/xml/dtd/common.xsd b/xml/dtd/common.xsd
index d71655d..798043e 100644
--- a/xml/dtd/common.xsd
+++ b/xml/dtd/common.xsd
@@ -104,7 +104,7 @@
         <xs:element ref="waiver_rep"/>
         <xs:element ref="poc1"/>
         <xs:group ref="address-group"/>
-        <xs:element ref="coc"/>
+        <xs:element ref="coc" minOccurs="0"/>
         <xs:element ref="invoice_rep"/>
         <xs:element ref="invoice_mail"/>
         <xs:element ref="invoice_extra_field" minOccurs="0"/>