diff --git a/gbcs-server/src/main/resources/net/woggioni/gbcs/server/schema/gbcs.xsd b/gbcs-server/src/main/resources/net/woggioni/gbcs/server/schema/gbcs.xsd
index 24445b2..5809ed4 100644
--- a/gbcs-server/src/main/resources/net/woggioni/gbcs/server/schema/gbcs.xsd
+++ b/gbcs-server/src/main/resources/net/woggioni/gbcs/server/schema/gbcs.xsd
@@ -107,7 +107,7 @@
         <xs:attribute name="calls" type="xs:positiveInteger" use="required"/>
         <xs:attribute name="period" type="xs:duration" use="required"/>
         <xs:attribute name="max-available-calls" type="xs:positiveInteger" use="optional"/>
-        <xs:attribute name="initial-available-calls" type="xs:positiveInteger" use="optional"/>
+        <xs:attribute name="initial-available-calls" type="xs:unsignedInt" use="optional"/>
     </xs:complexType>
 
     <xs:complexType name="anonymousUserType">