diff --git a/xsd/siri_model/siri_situationIdentity-v1.1.xsd b/xsd/siri_model/siri_situationIdentity-v1.1.xsd
index 9d8899bb..db32d9cf 100644
--- a/xsd/siri_model/siri_situationIdentity-v1.1.xsd
+++ b/xsd/siri_model/siri_situationIdentity-v1.1.xsd
@@ -1,9 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <xsd:schema xmlns="http://www.siri.org.uk/siri" xmlns:ifopt="http://www.ifopt.org.uk/ifopt" xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.siri.org.uk/siri" elementFormDefault="qualified" attributeFormDefault="unqualified" version="1.1" id="siri_situationIdentity">
- <!--
-12.06.2018 D. Rubli, Siri_XML-2.0p_a0.5:
-- ParticipantRef changed from optional to mandatory
--->
  <xsd:annotation>
   <xsd:appinfo>
    <Metadata xmlns="http://www.govtalk.gov.uk/CM/gms-xs">
@@ -150,7 +146,7 @@ Rail transport, Roads and road transport
      <xsd:documentation>Unique identifier of a Country of a Participant who created SITUATION. Provides namespace for Participant If absent proided from context.</xsd:documentation>
     </xsd:annotation>
    </xsd:element>
-   <xsd:element name="ParticipantRef" type="ParticipantRefStructure">
+   <xsd:element name="ParticipantRef" type="ParticipantRefStructure" minOccurs="0">
     <xsd:annotation>
      <xsd:documentation>Unique identifier of a Participant. Provides namespace for SITUATION. If absent provdied from context.</xsd:documentation>
     </xsd:annotation>