Error when create composite index in PostgreSQL using liquibase change log

Question

While trying to generate database using liquibase changelog in Postgres, I am getting following error:

forIndexName is not allowed on postgresql

Following is my change log which is generating same error:

<changeSet author="chintan.patel" id="CP0001">
        <createIndex indexName="PK_USER" tableName="USER" unique="true">
            <column name="FIRSTNAME"/>
            <column name="MIDDLENAME"/>
            <column name="LASTNAME"/>
        </createIndex>
        <addPrimaryKey columnNames="FIRSTNAME, MIDDLENAME, LASTNAME" constraintName="PK_USER" forIndexName="PK_USER" tableName="USER"/>
    </changeSet>

This same change set works fine in Oracle. Please suggest me, whats wrong here.