diff --git a/xsd/siri_model/siri_reference.xsd b/xsd/siri_model/siri_reference.xsd
index 5f5c897..13cd2e2 100644
--- a/xsd/siri_model/siri_reference.xsd
+++ b/xsd/siri_model/siri_reference.xsd
@@ -349,7 +349,11 @@ Rail transport, Roads and road transport
 			<xsd:enumeration value="ferry"/>
 			<xsd:enumeration value="metro"/>
 			<xsd:enumeration value="rail"/>
-			<xsd:enumeration value="taxi"/>
+			<xsd:enumeration value="taxi">
+				<xsd:annotation>
+   					<xsd:documentation>To be used to indicate that a scheduled service is operated by taxi. Should not be used to indicate a regular taxi-service.</xsd:documentation>
+				</xsd:annotation>
+			</xsd:enumeration>
 			<xsd:enumeration value="tram"/>
 			<xsd:enumeration value="underground"/>
 		</xsd:restriction>