diff --git a/doctrine-mapping.xsd b/doctrine-mapping.xsd
index c0c2d4623..e220ab714 100644
--- a/doctrine-mapping.xsd
+++ b/doctrine-mapping.xsd
@@ -419,9 +419,16 @@
     <xs:sequence>
       <xs:any minOccurs="0" maxOccurs="unbounded" namespace="##other"/>
     </xs:sequence>
-    <xs:attribute name="class" type="xs:string" use="required" />
+    <xs:attribute name="class" type="orm:fqcn" use="required" />
   </xs:complexType>
 
+  <xs:simpleType name="fqcn" id="fqcn">
+    <xs:restriction base="xs:token">
+      <xs:pattern value="[a-zA-Z_u01-uff][a-zA-Z0-9_u01-uff]+" id="fqcn.pattern">
+      </xs:pattern>
+    </xs:restriction>
+  </xs:simpleType>
+
   <xs:complexType name="inverse-join-columns">
     <xs:sequence>
       <xs:element name="join-column" type="orm:join-column" minOccurs="1" maxOccurs="unbounded" />