Case-Insensitive XQuery Fails. Non-Case-Insensitive Works

I am trying to edit my XQuery to perform a case-insensitive text comparison. Previously the XQuery worked just fine (it wasn't case-insensitive though) but now with the edit it doesn't find the element text.

Have I done something wrong?

Original XQuery that works fine:

ns:attributes/ns:text/ns:name[. = 'display name']/following-sibling::ns:value

New Case-Insensitive comparison that fails:

ns:attributes/ns:text/ns:name[fn:lower-case(text()) = 'display name']/following-sibling::ns:value

Any ideas what I am doing wrong?

The XML data structure looks like this:

 <attributes>
    <text>
      <name>display name</name>
      <value>Abc Def</value>
    </text>
  </attributes>