diff --git a/xml/dtd/common.xsd b/xml/dtd/common.xsd
index b00fc22..b9dcb70 100644
--- a/xml/dtd/common.xsd
+++ b/xml/dtd/common.xsd
@@ -83,7 +83,7 @@
   <xs:element name="coc">
     <xs:complexType>
       <xs:simpleContent>
-        <xs:extension base="xs:integer">
+        <xs:extension base="xs:string">
           <xs:attribute name="nationality" type="xs:string"/>
         </xs:extension>
       </xs:simpleContent>