Combination of RAND and [] yields error "The target variable of a BIND must not be used before the BIND clause"

[hannahbast]

The following query works if the [] is replaced by a variable, but produces the error from the title otherwise:

PREFIX wdt: <http://www.wikidata.org/prop/direct/>
SELECT * WHERE {
  SELECT ?subject {
    ?subject wdt:P31 []
  }
  ORDER BY RAND()
  LIMIT 1
}

https://qlever.cs.uni-freiburg.de/wikidata/DTNSyc